From: yangge yangge1116@126.com
If a large number of CMA memory are configured in system (for example, the CMA memory accounts for 50% of the system memory), starting a virtual virtual machine with device passthrough, it will call pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory. Normally if a page is present and in CMA area, pin_user_pages_remote() will migrate the page from CMA area to non-CMA area because of FOLL_LONGTERM flag. But the current code will cause the migration failure due to unexpected page refcounts, and eventually cause the virtual machine fail to start.
If a page is added in LRU batch, its refcount increases one, remove the page from LRU batch decreases one. Page migration requires the page is not referenced by others except page mapping. Before migrating a page, we should try to drain the page from LRU batch in case the page is in it, however, folio_test_lru() is not sufficient to tell whether the page is in LRU batch or not, if the page is in LRU batch, the migration will fail.
To solve the problem above, we modify the logic of adding to LRU batch. Before adding a page to LRU batch, we clear the LRU flag of the page so that we can check whether the page is in LRU batch by folio_test_lru(page). It's quite valuable, because likely we don't want to blindly drain the LRU batch simply because there is some unexpected reference on a page, as described above.
This change makes the LRU flag of a page invisible for longer, which may impact some programs. For example, as long as a page is on a LRU batch, we cannot isolate it, and we cannot check if it's an LRU page. Further, a page can now only be on exactly one LRU batch. This doesn't seem to matter much, because a new page is allocated from buddy and added to the lru batch, or be isolated, it's LRU flag may also be invisible for a long time.
Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Cc: stable@vger.kernel.org Signed-off-by: yangge yangge1116@126.com --- mm/swap.c | 43 +++++++++++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 12 deletions(-)
V4: Adjust commit message according to David's comments V3: Add fixes tag V2: Adjust code and commit message according to David's comments
diff --git a/mm/swap.c b/mm/swap.c index dc205bd..9caf6b0 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -211,10 +211,6 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) for (i = 0; i < folio_batch_count(fbatch); i++) { struct folio *folio = fbatch->folios[i];
- /* block memcg migration while the folio moves between lru */ - if (move_fn != lru_add_fn && !folio_test_clear_lru(folio)) - continue; - folio_lruvec_relock_irqsave(folio, &lruvec, &flags); move_fn(lruvec, folio);
@@ -255,11 +251,16 @@ static void lru_move_tail_fn(struct lruvec *lruvec, struct folio *folio) void folio_rotate_reclaimable(struct folio *folio) { if (!folio_test_locked(folio) && !folio_test_dirty(folio) && - !folio_test_unevictable(folio) && folio_test_lru(folio)) { + !folio_test_unevictable(folio)) { struct folio_batch *fbatch; unsigned long flags;
folio_get(folio); + if (!folio_test_clear_lru(folio)) { + folio_put(folio); + return; + } + local_lock_irqsave(&lru_rotate.lock, flags); fbatch = this_cpu_ptr(&lru_rotate.fbatch); folio_batch_add_and_move(fbatch, folio, lru_move_tail_fn); @@ -352,11 +353,15 @@ static void folio_activate_drain(int cpu)
void folio_activate(struct folio *folio) { - if (folio_test_lru(folio) && !folio_test_active(folio) && - !folio_test_unevictable(folio)) { + if (!folio_test_active(folio) && !folio_test_unevictable(folio)) { struct folio_batch *fbatch;
folio_get(folio); + if (!folio_test_clear_lru(folio)) { + folio_put(folio); + return; + } + local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.activate); folio_batch_add_and_move(fbatch, folio, folio_activate_fn); @@ -700,6 +705,11 @@ void deactivate_file_folio(struct folio *folio) return;
folio_get(folio); + if (!folio_test_clear_lru(folio)) { + folio_put(folio); + return; + } + local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.lru_deactivate_file); folio_batch_add_and_move(fbatch, folio, lru_deactivate_file_fn); @@ -716,11 +726,16 @@ void deactivate_file_folio(struct folio *folio) */ void folio_deactivate(struct folio *folio) { - if (folio_test_lru(folio) && !folio_test_unevictable(folio) && - (folio_test_active(folio) || lru_gen_enabled())) { + if (!folio_test_unevictable(folio) && (folio_test_active(folio) || + lru_gen_enabled())) { struct folio_batch *fbatch;
folio_get(folio); + if (!folio_test_clear_lru(folio)) { + folio_put(folio); + return; + } + local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.lru_deactivate); folio_batch_add_and_move(fbatch, folio, lru_deactivate_fn); @@ -737,12 +752,16 @@ void folio_deactivate(struct folio *folio) */ void folio_mark_lazyfree(struct folio *folio) { - if (folio_test_lru(folio) && folio_test_anon(folio) && - folio_test_swapbacked(folio) && !folio_test_swapcache(folio) && - !folio_test_unevictable(folio)) { + if (folio_test_anon(folio) && folio_test_swapbacked(folio) && + !folio_test_swapcache(folio) && !folio_test_unevictable(folio)) { struct folio_batch *fbatch;
folio_get(folio); + if (!folio_test_clear_lru(folio)) { + folio_put(folio); + return; + } + local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.lru_lazyfree); folio_batch_add_and_move(fbatch, folio, lru_lazyfree_fn);
Hi,
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
In addition, folio_mark_accessed() calls __lru_cache_activate_folio(). This function does as follow comments:
/* * Search backwards on the optimistic assumption that the folio being * activated has just been added to this batch. */
However, after this patch, folio without lru flag may be in other fbatch too, such as cpu_fbatches.activate.
在 2024/7/4 14:52, yangge1116@126.com 写道:
From: yangge yangge1116@126.com
If a large number of CMA memory are configured in system (for example, the CMA memory accounts for 50% of the system memory), starting a virtual virtual machine with device passthrough, it will call pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory. Normally if a page is present and in CMA area, pin_user_pages_remote() will migrate the page from CMA area to non-CMA area because of FOLL_LONGTERM flag. But the current code will cause the migration failure due to unexpected page refcounts, and eventually cause the virtual machine fail to start.
If a page is added in LRU batch, its refcount increases one, remove the page from LRU batch decreases one. Page migration requires the page is not referenced by others except page mapping. Before migrating a page, we should try to drain the page from LRU batch in case the page is in it, however, folio_test_lru() is not sufficient to tell whether the page is in LRU batch or not, if the page is in LRU batch, the migration will fail.
To solve the problem above, we modify the logic of adding to LRU batch. Before adding a page to LRU batch, we clear the LRU flag of the page so that we can check whether the page is in LRU batch by folio_test_lru(page). It's quite valuable, because likely we don't want to blindly drain the LRU batch simply because there is some unexpected reference on a page, as described above.
This change makes the LRU flag of a page invisible for longer, which may impact some programs. For example, as long as a page is on a LRU batch, we cannot isolate it, and we cannot check if it's an LRU page. Further, a page can now only be on exactly one LRU batch. This doesn't seem to matter much, because a new page is allocated from buddy and added to the lru batch, or be isolated, it's LRU flag may also be invisible for a long time.
Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Cc: stable@vger.kernel.org Signed-off-by: yangge yangge1116@126.com
mm/swap.c | 43 +++++++++++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 12 deletions(-)
V4: Adjust commit message according to David's comments V3: Add fixes tag V2: Adjust code and commit message according to David's comments
diff --git a/mm/swap.c b/mm/swap.c index dc205bd..9caf6b0 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -211,10 +211,6 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) for (i = 0; i < folio_batch_count(fbatch); i++) { struct folio *folio = fbatch->folios[i];
/* block memcg migration while the folio moves between lru */if (move_fn != lru_add_fn && !folio_test_clear_lru(folio))continue;- folio_lruvec_relock_irqsave(folio, &lruvec, &flags); move_fn(lruvec, folio);
@@ -255,11 +251,16 @@ static void lru_move_tail_fn(struct lruvec *lruvec, struct folio *folio) void folio_rotate_reclaimable(struct folio *folio) { if (!folio_test_locked(folio) && !folio_test_dirty(folio) &&
!folio_test_unevictable(folio) && folio_test_lru(folio)) {
!folio_test_unevictable(folio)) {folio_get(folio);
if (!folio_test_clear_lru(folio)) {folio_put(folio);return;}- local_lock_irqsave(&lru_rotate.lock, flags); fbatch = this_cpu_ptr(&lru_rotate.fbatch); folio_batch_add_and_move(fbatch, folio, lru_move_tail_fn);
@@ -352,11 +353,15 @@ static void folio_activate_drain(int cpu) void folio_activate(struct folio *folio) {
- if (folio_test_lru(folio) && !folio_test_active(folio) &&
!folio_test_unevictable(folio)) {
- if (!folio_test_active(folio) && !folio_test_unevictable(folio)) { struct folio_batch *fbatch;
folio_get(folio);
if (!folio_test_clear_lru(folio)) {folio_put(folio);return;}- local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.activate); folio_batch_add_and_move(fbatch, folio, folio_activate_fn);
@@ -700,6 +705,11 @@ void deactivate_file_folio(struct folio *folio) return; folio_get(folio);
- if (!folio_test_clear_lru(folio)) {
folio_put(folio);return;- }
- local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.lru_deactivate_file); folio_batch_add_and_move(fbatch, folio, lru_deactivate_file_fn);
@@ -716,11 +726,16 @@ void deactivate_file_folio(struct folio *folio) */ void folio_deactivate(struct folio *folio) {
- if (folio_test_lru(folio) && !folio_test_unevictable(folio) &&
(folio_test_active(folio) || lru_gen_enabled())) {
- if (!folio_test_unevictable(folio) && (folio_test_active(folio) ||
lru_gen_enabled())) {folio_get(folio);
if (!folio_test_clear_lru(folio)) {folio_put(folio);return;}- local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.lru_deactivate); folio_batch_add_and_move(fbatch, folio, lru_deactivate_fn);
@@ -737,12 +752,16 @@ void folio_deactivate(struct folio *folio) */ void folio_mark_lazyfree(struct folio *folio) {
- if (folio_test_lru(folio) && folio_test_anon(folio) &&
folio_test_swapbacked(folio) && !folio_test_swapcache(folio) &&!folio_test_unevictable(folio)) {
- if (folio_test_anon(folio) && folio_test_swapbacked(folio) &&
!folio_test_swapcache(folio) && !folio_test_unevictable(folio)) {folio_get(folio);
if (!folio_test_clear_lru(folio)) {folio_put(folio);return;}- local_lock(&cpu_fbatches.lock); fbatch = this_cpu_ptr(&cpu_fbatches.lru_lazyfree); folio_batch_add_and_move(fbatch, folio, lru_lazyfree_fn);
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
On 27.03.25 12:16, Jinjiang Tu wrote:
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
So the current behavior is that folio_mark_accessed() will end up calling folio_activate() once, and then __lru_cache_activate_folio() until the LRU was drained (which can take a looong time).
The old behavior was that folio_mark_accessed() would keep calling folio_activate() until the LRU was drained simply because it was full of "all the same pages" ?. Only *after* the LRU was drained, folio_mark_accessed() would actually not do anything (desired behavior).
So the overhead comes primarily from __lru_cache_activate_folio() searching through the list "more" repeatedly because the LRU does get drained less frequently; and it would never find it in there in this case.
So ... it used to be suboptimal before, now it's more suboptimal I guess?! :)
We'd need a way to better identify "this folio is already queued for activation". Searching that list as well would be one option, but the hole "search the list" is nasty.
Maybe we can simply set the folio as active when staging it for activation, after having cleared the LRU flag? We already do that during folio_add.
As the LRU flag was cleared, nobody should be messing with that folio until the cache was drained and the move was successful.
Pretty sure this doesn't work, but just to throw out an idea:
From c26e1c0ceda6c818826e5b89dc7c7c9279138f80 Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Tue, 1 Apr 2025 16:31:56 +0200 Subject: [PATCH] test
Signed-off-by: David Hildenbrand david@redhat.com --- mm/swap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c index fc8281ef42415..bbf9aa76db87f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -175,6 +175,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) folios_put(fbatch); }
+static void lru_activate(struct lruvec *lruvec, struct folio *folio); + static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, struct folio *folio, move_fn_t move_fn, bool on_lru, bool disable_irq) @@ -191,6 +193,10 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, else local_lock(&cpu_fbatches.lock);
+ /* We'll only perform the actual list move deferred. */ + if (move_fn == lru_activate) + folio_set_active(folio); + if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); @@ -299,12 +305,14 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) { long nr_pages = folio_nr_pages(folio);
- if (folio_test_active(folio) || folio_test_unevictable(folio)) - return; - + /* + * We set the folio active after clearing the LRU flag, and set the + * LRU flag only after moving it to the right list. + */ + VM_WARN_ON_ONCE(!folio_test_active(folio)); + VM_WARN_ON_ONCE(folio_test_unevictable(folio));
lruvec_del_folio(lruvec, folio); - folio_set_active(folio); lruvec_add_folio(lruvec, folio); trace_mm_lru_activate(folio);
@@ -342,7 +350,10 @@ void folio_activate(struct folio *folio) return;
lruvec = folio_lruvec_lock_irq(folio); - lru_activate(lruvec, folio); + if (!folio_test_unevictable(folio)) { + folio_set_active(folio); + lru_activate(lruvec, folio); + } unlock_page_lruvec_irq(lruvec); folio_set_lru(folio); }
在 2025/4/1 22:33, David Hildenbrand 写道:
On 27.03.25 12:16, Jinjiang Tu wrote:
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
So the current behavior is that folio_mark_accessed() will end up calling folio_activate() once, and then __lru_cache_activate_folio() until the LRU was drained (which can take a looong time).
The old behavior was that folio_mark_accessed() would keep calling folio_activate() until the LRU was drained simply because it was full of "all the same pages" ?. Only *after* the LRU was drained, folio_mark_accessed() would actually not do anything (desired behavior).
So the overhead comes primarily from __lru_cache_activate_folio() searching through the list "more" repeatedly because the LRU does get drained less frequently; and it would never find it in there in this case.
So ... it used to be suboptimal before, now it's more suboptimal I guess?! :)
We'd need a way to better identify "this folio is already queued for activation". Searching that list as well would be one option, but the hole "search the list" is nasty.
Sorry for late reply. I tried to search the activate batch with the following diff, and the performance regression disappears.
diff --git a/mm/swap.c b/mm/swap.c index f81c8aa93e67..cfe484ff12e6 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -400,6 +400,21 @@ static void __lru_cache_activate_folio(struct folio *folio) } }
+ fbatch = this_cpu_ptr(&cpu_fbatches.activate); + for (i = folio_batch_count(fbatch) - 1; i >= 0; i--) { + struct folio *batch_folio = fbatch->folios[i]; + + if (batch_folio == folio) { + struct lruvec *lruvec; + unsigned long flags; + + lruvec = folio_lruvec_lock_irqsave(folio, &flags); + folio_activate_fn(lruvec, folio); + unlock_page_lruvec_irqrestore(lruvec, flags); + break; + } + } + local_unlock(&cpu_fbatches.lock); }
Maybe we can simply set the folio as active when staging it for activation, after having cleared the LRU flag? We already do that during folio_add.
As the LRU flag was cleared, nobody should be messing with that folio until the cache was drained and the move was successful.
Yes, anyone who wants to delete the folio from lru list should test LRU flag
I look some folio_test_active() calls, madvise_cold_or_pageout_pte_range() will set workingset flag if active flag is set. It seems more reasonable if we set active flag after adding to activate batch, since adding to activate batch already means active.
Pretty sure this doesn't work, but just to throw out an idea:
Thanks, I will try it ASAP.
From c26e1c0ceda6c818826e5b89dc7c7c9279138f80 Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Tue, 1 Apr 2025 16:31:56 +0200 Subject: [PATCH] test
Signed-off-by: David Hildenbrand david@redhat.com
mm/swap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c index fc8281ef42415..bbf9aa76db87f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -175,6 +175,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) folios_put(fbatch); }
+static void lru_activate(struct lruvec *lruvec, struct folio *folio);
static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, struct folio *folio, move_fn_t move_fn, bool on_lru, bool disable_irq) @@ -191,6 +193,10 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, else local_lock(&cpu_fbatches.lock);
+ /* We'll only perform the actual list move deferred. */ + if (move_fn == lru_activate) + folio_set_active(folio);
if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); @@ -299,12 +305,14 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) { long nr_pages = folio_nr_pages(folio);
- if (folio_test_active(folio) || folio_test_unevictable(folio)) - return;
+ /* + * We set the folio active after clearing the LRU flag, and set the + * LRU flag only after moving it to the right list. + */ + VM_WARN_ON_ONCE(!folio_test_active(folio)); + VM_WARN_ON_ONCE(folio_test_unevictable(folio));
lruvec_del_folio(lruvec, folio); - folio_set_active(folio); lruvec_add_folio(lruvec, folio); trace_mm_lru_activate(folio);
@@ -342,7 +350,10 @@ void folio_activate(struct folio *folio) return;
lruvec = folio_lruvec_lock_irq(folio); - lru_activate(lruvec, folio); + if (!folio_test_unevictable(folio)) { + folio_set_active(folio); + lru_activate(lruvec, folio); + } unlock_page_lruvec_irq(lruvec); folio_set_lru(folio); }
在 2025/4/1 22:33, David Hildenbrand 写道:
On 27.03.25 12:16, Jinjiang Tu wrote:
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
So the current behavior is that folio_mark_accessed() will end up calling folio_activate() once, and then __lru_cache_activate_folio() until the LRU was drained (which can take a looong time).
The old behavior was that folio_mark_accessed() would keep calling folio_activate() until the LRU was drained simply because it was full of "all the same pages" ?. Only *after* the LRU was drained, folio_mark_accessed() would actually not do anything (desired behavior).
So the overhead comes primarily from __lru_cache_activate_folio() searching through the list "more" repeatedly because the LRU does get drained less frequently; and it would never find it in there in this case.
So ... it used to be suboptimal before, now it's more suboptimal I guess?! :)
We'd need a way to better identify "this folio is already queued for activation". Searching that list as well would be one option, but the hole "search the list" is nasty.
Maybe we can simply set the folio as active when staging it for activation, after having cleared the LRU flag? We already do that during folio_add.
As the LRU flag was cleared, nobody should be messing with that folio until the cache was drained and the move was successful.
Pretty sure this doesn't work, but just to throw out an idea:
From c26e1c0ceda6c818826e5b89dc7c7c9279138f80 Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Tue, 1 Apr 2025 16:31:56 +0200 Subject: [PATCH] test
Signed-off-by: David Hildenbrand david@redhat.com
mm/swap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c index fc8281ef42415..bbf9aa76db87f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -175,6 +175,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) folios_put(fbatch); }
+static void lru_activate(struct lruvec *lruvec, struct folio *folio);
static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, struct folio *folio, move_fn_t move_fn, bool on_lru, bool disable_irq) @@ -191,6 +193,10 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, else local_lock(&cpu_fbatches.lock);
+ /* We'll only perform the actual list move deferred. */ + if (move_fn == lru_activate) + folio_set_active(folio);
if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); @@ -299,12 +305,14 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) { long nr_pages = folio_nr_pages(folio);
- if (folio_test_active(folio) || folio_test_unevictable(folio)) - return;
+ /* + * We set the folio active after clearing the LRU flag, and set the + * LRU flag only after moving it to the right list. + */ + VM_WARN_ON_ONCE(!folio_test_active(folio)); + VM_WARN_ON_ONCE(folio_test_unevictable(folio));
lruvec_del_folio(lruvec, folio); - folio_set_active(folio); lruvec_add_folio(lruvec, folio); trace_mm_lru_activate(folio);
@@ -342,7 +350,10 @@ void folio_activate(struct folio *folio) return;
lruvec = folio_lruvec_lock_irq(folio); - lru_activate(lruvec, folio); + if (!folio_test_unevictable(folio)) { + folio_set_active(folio); + lru_activate(lruvec, folio); + } unlock_page_lruvec_irq(lruvec); folio_set_lru(folio); }
I test with the patch, and the performance regression disappears.
By the way, I find folio_test_unevictable() is called in lru_deactivate, lru_lazyfree, etc. unevictable flag is set when the caller clears lru flag. IIUC, since commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch"), folios in fbatch can't be set unevictable flag, so there is no need to check unevictable flag in lru_deactivate, lru_lazyfree, etc?
On 08.04.25 10:47, Jinjiang Tu wrote:
在 2025/4/1 22:33, David Hildenbrand 写道:
On 27.03.25 12:16, Jinjiang Tu wrote:
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
So the current behavior is that folio_mark_accessed() will end up calling folio_activate() once, and then __lru_cache_activate_folio() until the LRU was drained (which can take a looong time).
The old behavior was that folio_mark_accessed() would keep calling folio_activate() until the LRU was drained simply because it was full of "all the same pages" ?. Only *after* the LRU was drained, folio_mark_accessed() would actually not do anything (desired behavior).
So the overhead comes primarily from __lru_cache_activate_folio() searching through the list "more" repeatedly because the LRU does get drained less frequently; and it would never find it in there in this case.
So ... it used to be suboptimal before, now it's more suboptimal I guess?! :)
We'd need a way to better identify "this folio is already queued for activation". Searching that list as well would be one option, but the hole "search the list" is nasty.
Maybe we can simply set the folio as active when staging it for activation, after having cleared the LRU flag? We already do that during folio_add.
As the LRU flag was cleared, nobody should be messing with that folio until the cache was drained and the move was successful.
Pretty sure this doesn't work, but just to throw out an idea:
From c26e1c0ceda6c818826e5b89dc7c7c9279138f80 Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Tue, 1 Apr 2025 16:31:56 +0200 Subject: [PATCH] test
Signed-off-by: David Hildenbrand david@redhat.com
mm/swap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c index fc8281ef42415..bbf9aa76db87f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -175,6 +175,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) folios_put(fbatch); }
+static void lru_activate(struct lruvec *lruvec, struct folio *folio);
static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, struct folio *folio, move_fn_t move_fn, bool on_lru, bool disable_irq) @@ -191,6 +193,10 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, else local_lock(&cpu_fbatches.lock);
+ /* We'll only perform the actual list move deferred. */ + if (move_fn == lru_activate) + folio_set_active(folio);
if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); @@ -299,12 +305,14 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) { long nr_pages = folio_nr_pages(folio);
- if (folio_test_active(folio) || folio_test_unevictable(folio)) - return;
+ /* + * We set the folio active after clearing the LRU flag, and set the + * LRU flag only after moving it to the right list. + */ + VM_WARN_ON_ONCE(!folio_test_active(folio)); + VM_WARN_ON_ONCE(folio_test_unevictable(folio));
lruvec_del_folio(lruvec, folio); - folio_set_active(folio); lruvec_add_folio(lruvec, folio); trace_mm_lru_activate(folio);
@@ -342,7 +350,10 @@ void folio_activate(struct folio *folio) return;
lruvec = folio_lruvec_lock_irq(folio); - lru_activate(lruvec, folio); + if (!folio_test_unevictable(folio)) { + folio_set_active(folio); + lru_activate(lruvec, folio); + } unlock_page_lruvec_irq(lruvec); folio_set_lru(folio); }
I test with the patch, and the performance regression disappears.
By the way, I find folio_test_unevictable() is called in lru_deactivate, lru_lazyfree, etc. unevictable flag is set when the caller clears lru flag. IIUC, since commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch"), folios in fbatch can't be set unevictable flag, so there is no need to check unevictable flag in lru_deactivate, lru_lazyfree, etc?
I was asking myself the exact same question when crafting this patch. Sounds like a cleanup worth investigating! :)
Do you have capacity to look into that, and to turn my proposal into a proper patch? It might take me a bit until I get to it.
在 2025/4/8 18:04, David Hildenbrand 写道:
On 08.04.25 10:47, Jinjiang Tu wrote:
在 2025/4/1 22:33, David Hildenbrand 写道:
On 27.03.25 12:16, Jinjiang Tu wrote:
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
So the current behavior is that folio_mark_accessed() will end up calling folio_activate() once, and then __lru_cache_activate_folio() until the LRU was drained (which can take a looong time).
The old behavior was that folio_mark_accessed() would keep calling folio_activate() until the LRU was drained simply because it was full of "all the same pages" ?. Only *after* the LRU was drained, folio_mark_accessed() would actually not do anything (desired behavior).
So the overhead comes primarily from __lru_cache_activate_folio() searching through the list "more" repeatedly because the LRU does get drained less frequently; and it would never find it in there in this case.
So ... it used to be suboptimal before, now it's more suboptimal I guess?! :)
We'd need a way to better identify "this folio is already queued for activation". Searching that list as well would be one option, but the hole "search the list" is nasty.
Maybe we can simply set the folio as active when staging it for activation, after having cleared the LRU flag? We already do that during folio_add.
As the LRU flag was cleared, nobody should be messing with that folio until the cache was drained and the move was successful.
Pretty sure this doesn't work, but just to throw out an idea:
From c26e1c0ceda6c818826e5b89dc7c7c9279138f80 Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Tue, 1 Apr 2025 16:31:56 +0200 Subject: [PATCH] test
Signed-off-by: David Hildenbrand david@redhat.com
mm/swap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c index fc8281ef42415..bbf9aa76db87f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -175,6 +175,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) folios_put(fbatch); }
+static void lru_activate(struct lruvec *lruvec, struct folio *folio);
static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, struct folio *folio, move_fn_t move_fn, bool on_lru, bool disable_irq) @@ -191,6 +193,10 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, else local_lock(&cpu_fbatches.lock);
+ /* We'll only perform the actual list move deferred. */ + if (move_fn == lru_activate) + folio_set_active(folio);
if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); @@ -299,12 +305,14 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) { long nr_pages = folio_nr_pages(folio);
- if (folio_test_active(folio) || folio_test_unevictable(folio)) - return;
+ /* + * We set the folio active after clearing the LRU flag, and set the + * LRU flag only after moving it to the right list. + */ + VM_WARN_ON_ONCE(!folio_test_active(folio)); + VM_WARN_ON_ONCE(folio_test_unevictable(folio));
lruvec_del_folio(lruvec, folio); - folio_set_active(folio); lruvec_add_folio(lruvec, folio); trace_mm_lru_activate(folio);
@@ -342,7 +350,10 @@ void folio_activate(struct folio *folio) return;
lruvec = folio_lruvec_lock_irq(folio); - lru_activate(lruvec, folio); + if (!folio_test_unevictable(folio)) { + folio_set_active(folio); + lru_activate(lruvec, folio); + } unlock_page_lruvec_irq(lruvec); folio_set_lru(folio); }
I test with the patch, and the performance regression disappears.
By the way, I find folio_test_unevictable() is called in lru_deactivate, lru_lazyfree, etc. unevictable flag is set when the caller clears lru flag. IIUC, since commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch"), folios in fbatch can't be set unevictable flag, so there is no need to check unevictable flag in lru_deactivate, lru_lazyfree, etc?
I was asking myself the exact same question when crafting this patch. Sounds like a cleanup worth investigating! :)
Do you have capacity to look into that, and to turn my proposal into a proper patch? It might take me a bit until I get to it.
Sure, I will send a formal patch ASAP.
在 2025/4/8 18:04, David Hildenbrand 写道:
On 08.04.25 10:47, Jinjiang Tu wrote:
在 2025/4/1 22:33, David Hildenbrand 写道:
On 27.03.25 12:16, Jinjiang Tu wrote:
在 2025/3/26 20:46, David Hildenbrand 写道:
On 26.03.25 13:42, Jinjiang Tu wrote:
Hi,
Hi!
We notiched a 12.3% performance regression for LibMicro pwrite testcase due to commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch").
The testcase is executed as follows, and the file is tmpfs file. pwrite -E -C 200 -L -S -W -N "pwrite_t1k" -s 1k -I 500 -f $TFILE
Do we know how much that reflects real workloads? (IOW, how much should we care)
No, it's hard to say.
this testcase writes 1KB (only one page) to the tmpfs and repeats this step for many times. The Flame graph shows the performance regression comes from folio_mark_accessed() and workingset_activation().
folio_mark_accessed() is called for the same page for many times. Before this patch, each call will add the page to cpu_fbatches.activate. When the fbatch is full, the fbatch is drained and the page is promoted to active list. And then, folio_mark_accessed() does nothing in later calls.
But after this patch, the folio clear lru flags after it is added to cpu_fbatches.activate. After then, folio_mark_accessed will never call folio_activate() again due to the page is without lru flag, and the fbatch will not be full and the folio will not be marked active, later folio_mark_accessed() calls will always call workingset_activation(), leading to performance regression.
Would there be a good place to drain the LRU to effectively get that processed? (we can always try draining if the LRU flag is not set)
Maybe we could drain the search the cpu_fbatches.activate of the local cpu in __lru_cache_activate_folio()? Drain other fbatches is meaningless .
So the current behavior is that folio_mark_accessed() will end up calling folio_activate() once, and then __lru_cache_activate_folio() until the LRU was drained (which can take a looong time).
The old behavior was that folio_mark_accessed() would keep calling folio_activate() until the LRU was drained simply because it was full of "all the same pages" ?. Only *after* the LRU was drained, folio_mark_accessed() would actually not do anything (desired behavior).
So the overhead comes primarily from __lru_cache_activate_folio() searching through the list "more" repeatedly because the LRU does get drained less frequently; and it would never find it in there in this case.
So ... it used to be suboptimal before, now it's more suboptimal I guess?! :)
We'd need a way to better identify "this folio is already queued for activation". Searching that list as well would be one option, but the hole "search the list" is nasty.
Maybe we can simply set the folio as active when staging it for activation, after having cleared the LRU flag? We already do that during folio_add.
As the LRU flag was cleared, nobody should be messing with that folio until the cache was drained and the move was successful.
Pretty sure this doesn't work, but just to throw out an idea:
From c26e1c0ceda6c818826e5b89dc7c7c9279138f80 Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Tue, 1 Apr 2025 16:31:56 +0200 Subject: [PATCH] test
Signed-off-by: David Hildenbrand david@redhat.com
mm/swap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c index fc8281ef42415..bbf9aa76db87f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -175,6 +175,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) folios_put(fbatch); }
+static void lru_activate(struct lruvec *lruvec, struct folio *folio);
static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, struct folio *folio, move_fn_t move_fn, bool on_lru, bool disable_irq) @@ -191,6 +193,10 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, else local_lock(&cpu_fbatches.lock);
+ /* We'll only perform the actual list move deferred. */ + if (move_fn == lru_activate) + folio_set_active(folio);
if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); @@ -299,12 +305,14 @@ static void lru_activate(struct lruvec *lruvec, struct folio *folio) { long nr_pages = folio_nr_pages(folio);
- if (folio_test_active(folio) || folio_test_unevictable(folio)) - return;
+ /* + * We set the folio active after clearing the LRU flag, and set the + * LRU flag only after moving it to the right list. + */ + VM_WARN_ON_ONCE(!folio_test_active(folio)); + VM_WARN_ON_ONCE(folio_test_unevictable(folio));
lruvec_del_folio(lruvec, folio); - folio_set_active(folio); lruvec_add_folio(lruvec, folio); trace_mm_lru_activate(folio);
@@ -342,7 +350,10 @@ void folio_activate(struct folio *folio) return;
lruvec = folio_lruvec_lock_irq(folio); - lru_activate(lruvec, folio); + if (!folio_test_unevictable(folio)) { + folio_set_active(folio); + lru_activate(lruvec, folio); + } unlock_page_lruvec_irq(lruvec); folio_set_lru(folio); }
I test with the patch, and the performance regression disappears.
By the way, I find folio_test_unevictable() is called in lru_deactivate, lru_lazyfree, etc. unevictable flag is set when the caller clears lru flag. IIUC, since commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch"), folios in fbatch can't be set unevictable flag, so there is no need to check unevictable flag in lru_deactivate, lru_lazyfree, etc?
I was asking myself the exact same question when crafting this patch. Sounds like a cleanup worth investigating! :)
folio_activate __mlock_folio folio_test_unevictable folio_test_clear_lru folio_set_unevictable folio_set_lru folio_batch_add_and_move folio_test_clear_lru
In the above case, unevictable flag will be set before lru flag is cleared in folio_activate(). So folio may still be unevictable in lru_activate().
Do you have capacity to look into that, and to turn my proposal into a proper patch? It might take me a bit until I get to it.
linux-stable-mirror@lists.linaro.org
-
David Hildenbrand -
Jinjiang Tu -
yangge1116＠126.com