From: Kairui Song kasong@tencent.com

commit de60fd8ddeda2b41fbe11df11733838c5f684616 upstream.

xas_split_alloc could fail with NOMEM, and in such case, it should abort early instead of keep going and fail the xas_split below.

Link: https://lkml.kernel.org/r/20240416071722.45997-1-ryncsn@gmail.com Link: https://lkml.kernel.org/r/20240415171857.19244-1-ryncsn@gmail.com Link: https://lkml.kernel.org/r/20240415171857.19244-2-ryncsn@gmail.com Signed-off-by: Kairui Song kasong@tencent.com Acked-by: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Stable-dep-of: 6758c1128ceb ("mm/filemap: optimize filemap folio adding") --- mm/filemap.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c index 2809b1174f04..f85c13a1b739 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -867,9 +867,12 @@ noinline int __filemap_add_folio(struct address_space *mapping, unsigned int order = xa_get_order(xas.xa, xas.xa_index); void *entry, *old = NULL;

- if (order > folio_order(folio)) + if (order > folio_order(folio)) { xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index), order, gfp); + if (xas_error(&xas)) + goto error; + } xas_lock_irq(&xas); xas_for_each_conflict(&xas, entry) { old = entry;

From: Kairui Song kasong@tencent.com

commit 6758c1128ceb45d1a35298912b974eb4895b7dd9 upstream.

Instead of doing multiple tree walks, do one optimism range check with lock hold, and exit if raced with another insertion. If a shadow exists, check it with a new xas_get_order helper before releasing the lock to avoid redundant tree walks for getting its order.

Drop the lock and do the allocation only if a split is needed.

In the best case, it only need to walk the tree once. If it needs to alloc and split, 3 walks are issued (One for first ranged conflict check and order retrieving, one for the second check after allocation, one for the insert after split).

Testing with 4K pages, in an 8G cgroup, with 16G brd as block device:

echo 3 > /proc/sys/vm/drop_caches

fio -name=cached --numjobs=16 --filename=/mnt/test.img \ --buffered=1 --ioengine=mmap --rw=randread --time_based \ --ramp_time=30s --runtime=5m --group_reporting

Before: bw ( MiB/s): min= 1027, max= 3520, per=100.00%, avg=2445.02, stdev=18.90, samples=8691 iops : min=263001, max=901288, avg=625924.36, stdev=4837.28, samples=8691

After (+7.3%): bw ( MiB/s): min= 493, max= 3947, per=100.00%, avg=2625.56, stdev=25.74, samples=8651 iops : min=126454, max=1010681, avg=672142.61, stdev=6590.48, samples=8651

Test result with THP (do a THP randread then switch to 4K page in hope it issues a lot of splitting):

echo 3 > /proc/sys/vm/drop_caches

fio -name=cached --numjobs=16 --filename=/mnt/test.img \ --buffered=1 --ioengine=mmap -thp=1 --readonly \ --rw=randread --time_based --ramp_time=30s --runtime=10m \ --group_reporting

fio -name=cached --numjobs=16 --filename=/mnt/test.img \ --buffered=1 --ioengine=mmap \ --rw=randread --time_based --runtime=5s --group_reporting

Before: bw ( KiB/s): min= 4141, max=14202, per=100.00%, avg=7935.51, stdev=96.85, samples=18976 iops : min= 1029, max= 3548, avg=1979.52, stdev=24.23, samples=18976·

READ: bw=4545B/s (4545B/s), 4545B/s-4545B/s (4545B/s-4545B/s), io=64.0KiB (65.5kB), run=14419-14419msec

After (+12.5%): bw ( KiB/s): min= 4611, max=15370, per=100.00%, avg=8928.74, stdev=105.17, samples=19146 iops : min= 1151, max= 3842, avg=2231.27, stdev=26.29, samples=19146

READ: bw=4635B/s (4635B/s), 4635B/s-4635B/s (4635B/s-4635B/s), io=64.0KiB (65.5kB), run=14137-14137msec

The performance is better for both 4K (+7.5%) and THP (+12.5%) cached read.

Link: https://lkml.kernel.org/r/20240415171857.19244-5-ryncsn@gmail.com Signed-off-by: Kairui Song kasong@tencent.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Closes: https://lore.kernel.org/linux-mm/A5A976CB-DB57-4513-A700-656580488AB6@flying... [ kasong@tencent.com: minor adjustment of variable declarations ] --- lib/test_xarray.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++ mm/filemap.c | 53 +++++++++++++++++++++++++++++++----------- 2 files changed, 98 insertions(+), 14 deletions(-)

diff --git a/lib/test_xarray.c b/lib/test_xarray.c index 2e229012920b..542926da61a3 100644 --- a/lib/test_xarray.c +++ b/lib/test_xarray.c @@ -1789,6 +1789,64 @@ static noinline void check_xas_get_order(struct xarray *xa) } }

+static noinline void check_xas_conflict_get_order(struct xarray *xa) +{ + XA_STATE(xas, xa, 0); + + void *entry; + int only_once; + unsigned int max_order = IS_ENABLED(CONFIG_XARRAY_MULTI) ? 20 : 1; + unsigned int order; + unsigned long i, j, k; + + for (order = 0; order < max_order; order++) { + for (i = 0; i < 10; i++) { + xas_set_order(&xas, i << order, order); + do { + xas_lock(&xas); + xas_store(&xas, xa_mk_value(i)); + xas_unlock(&xas); + } while (xas_nomem(&xas, GFP_KERNEL)); + + /* + * Ensure xas_get_order works with xas_for_each_conflict. + */ + j = i << order; + for (k = 0; k < order; k++) { + only_once = 0; + xas_set_order(&xas, j + (1 << k), k); + xas_lock(&xas); + xas_for_each_conflict(&xas, entry) { + XA_BUG_ON(xa, entry != xa_mk_value(i)); + XA_BUG_ON(xa, xas_get_order(&xas) != order); + only_once++; + } + XA_BUG_ON(xa, only_once != 1); + xas_unlock(&xas); + } + + if (order < max_order - 1) { + only_once = 0; + xas_set_order(&xas, (i & ~1UL) << order, order + 1); + xas_lock(&xas); + xas_for_each_conflict(&xas, entry) { + XA_BUG_ON(xa, entry != xa_mk_value(i)); + XA_BUG_ON(xa, xas_get_order(&xas) != order); + only_once++; + } + XA_BUG_ON(xa, only_once != 1); + xas_unlock(&xas); + } + + xas_set_order(&xas, i << order, order); + xas_lock(&xas); + xas_store(&xas, NULL); + xas_unlock(&xas); + } + } +} + + static noinline void check_destroy(struct xarray *xa) { unsigned long index; @@ -1839,6 +1897,7 @@ static int xarray_checks(void) check_multi_store(&array); check_get_order(&array); check_xas_get_order(&array); + check_xas_conflict_get_order(&array); check_xa_alloc(); check_find(&array); check_find_entry(&array); diff --git a/mm/filemap.c b/mm/filemap.c index f85c13a1b739..d3b925232a59 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -841,6 +841,8 @@ noinline int __filemap_add_folio(struct address_space *mapping, { XA_STATE(xas, &mapping->i_pages, index); int huge = folio_test_hugetlb(folio); + void *alloced_shadow = NULL; + int alloced_order = 0; bool charged = false; long nr = 1;

@@ -863,16 +865,10 @@ noinline int __filemap_add_folio(struct address_space *mapping, folio->mapping = mapping; folio->index = xas.xa_index;

- do { - unsigned int order = xa_get_order(xas.xa, xas.xa_index); + for (;;) { + int order = -1, split_order = 0; void *entry, *old = NULL;

- if (order > folio_order(folio)) { - xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index), - order, gfp); - if (xas_error(&xas)) - goto error; - } xas_lock_irq(&xas); xas_for_each_conflict(&xas, entry) { old = entry; @@ -880,19 +876,33 @@ noinline int __filemap_add_folio(struct address_space *mapping, xas_set_err(&xas, -EEXIST); goto unlock; } + /* + * If a larger entry exists, + * it will be the first and only entry iterated. + */ + if (order == -1) + order = xas_get_order(&xas); + } + + /* entry may have changed before we re-acquire the lock */ + if (alloced_order && (old != alloced_shadow || order != alloced_order)) { + xas_destroy(&xas); + alloced_order = 0; }

if (old) { - if (shadowp) - *shadowp = old; - /* entry may have been split before we acquired lock */ - order = xa_get_order(xas.xa, xas.xa_index); - if (order > folio_order(folio)) { + if (order > 0 && order > folio_order(folio)) { /* How to handle large swap entries? */ BUG_ON(shmem_mapping(mapping)); + if (!alloced_order) { + split_order = order; + goto unlock; + } xas_split(&xas, old, order); xas_reset(&xas); } + if (shadowp) + *shadowp = old; }

xas_store(&xas, folio); @@ -908,9 +918,24 @@ noinline int __filemap_add_folio(struct address_space *mapping, __lruvec_stat_mod_folio(folio, NR_FILE_THPS, nr); } + unlock: xas_unlock_irq(&xas); - } while (xas_nomem(&xas, gfp)); + + /* split needed, alloc here and retry. */ + if (split_order) { + xas_split_alloc(&xas, old, split_order, gfp); + if (xas_error(&xas)) + goto error; + alloced_shadow = old; + alloced_order = split_order; + xas_reset(&xas); + continue; + } + + if (!xas_nomem(&xas, gfp)) + break; + }

if (xas_error(&xas)) goto error;