From: Zi Yan ziy@nvidia.com
In isolate_migratepages_block, when cc->alloc_contig is true, we are able to isolate compound pages, nr_migratepages and nr_isolated did not count compound pages correctly, causing us to isolate more pages than we thought. Count compound pages as the number of base pages they contain. Otherwise, we might be trapped in too_many_isolated while loop, since the actual isolated pages can go up to COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32, since we stop isolation after cc->nr_migratepages reaches to COMPACT_CLUSTER_MAX.
In addition, after we fix the issue above, cc->nr_migratepages could never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated, thus page isolation could not stop as we intended. Change the isolation stop condition to >=.
The issue can be triggered as follows: In a system with 16GB memory and an 8GB CMA region reserved by hugetlb_cma, if we first allocate 10GB THPs and mlock them (so some THPs are allocated in the CMA region and mlocked), reserving 6 1GB hugetlb pages via /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages will get stuck (looping in too_many_isolated function) until we kill either task. With the patch applied, oom will kill the application with 10GB THPs and let hugetlb page reservation finish.
Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) Signed-off-by: Zi Yan ziy@nvidia.com Reviewed-by: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org --- mm/compaction.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c index ee1f8439369e..3e834ac402f1 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
isolate_success: list_add(&page->lru, &cc->migratepages); - cc->nr_migratepages++; - nr_isolated++; + cc->nr_migratepages += compound_nr(page); + nr_isolated += compound_nr(page);
/* * Avoid isolating too much unless this block is being @@ -1021,7 +1021,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, * or a lock is contended. For contention, isolate quickly to * potentially remove one source of contention. */ - if (cc->nr_migratepages == COMPACT_CLUSTER_MAX && + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX && !cc->rescan && !cc->contended) { ++low_pfn; break; @@ -1132,7 +1132,7 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, if (!pfn) break;
- if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX) break; }
From: Zi Yan ziy@nvidia.com
In isolate_migratepages_block, if we have too many isolated pages and nr_migratepages is not zero, we should try to migrate what we have without wasting time on isolating.
Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) Suggested-by: Vlastimil Babka vbabka@suse.cz Signed-off-by: Zi Yan ziy@nvidia.com Cc: stable@vger.kernel.org --- mm/compaction.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c index 3e834ac402f1..4d237a7c3830 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -817,6 +817,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, * delay for some time until fewer pages are isolated */ while (unlikely(too_many_isolated(pgdat))) { + /* stop isolation if there are still pages not migrated */ + if (cc->nr_migratepages) + return 0; + /* async migration should just abort */ if (cc->mode == MIGRATE_ASYNC) return 0;
On 10/30/20 7:38 PM, Zi Yan wrote:
From: Zi Yan ziy@nvidia.com
In isolate_migratepages_block, if we have too many isolated pages and nr_migratepages is not zero, we should try to migrate what we have without wasting time on isolating.
As you CC stable, there should be a stronger reason (strictly speaking the problem should have been observed in practice, but this is a simple patch, so they could accept it), so I suggest Andrew adds the following paragraph:
In theory it's possible that multiple parallel compactions will cause too_many_isolated() to become true even if each has isolated less than COMPACT_CLUSTER_MAX, and loop forever in the while loop. Bailing immediately prevents that.
Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) Suggested-by: Vlastimil Babka vbabka@suse.cz Signed-off-by: Zi Yan ziy@nvidia.com Cc: stable@vger.kernel.org
Acked-by: Vlastimil Babka vbabka@suse.cz
mm/compaction.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c index 3e834ac402f1..4d237a7c3830 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -817,6 +817,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, * delay for some time until fewer pages are isolated */ while (unlikely(too_many_isolated(pgdat))) {
/* stop isolation if there are still pages not migrated */if (cc->nr_migratepages)return 0;- /* async migration should just abort */ if (cc->mode == MIGRATE_ASYNC) return 0;
On 10/30/20 7:38 PM, Zi Yan wrote:
From: Zi Yan ziy@nvidia.com
In isolate_migratepages_block, when cc->alloc_contig is true, we are able to isolate compound pages, nr_migratepages and nr_isolated did not count compound pages correctly, causing us to isolate more pages than we thought. Count compound pages as the number of base pages they contain. Otherwise, we might be trapped in too_many_isolated while loop, since the actual isolated pages can go up to COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32, since we stop isolation after cc->nr_migratepages reaches to COMPACT_CLUSTER_MAX.
In addition, after we fix the issue above, cc->nr_migratepages could never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated, thus page isolation could not stop as we intended. Change the isolation stop condition to >=.
The issue can be triggered as follows: In a system with 16GB memory and an 8GB CMA region reserved by hugetlb_cma, if we first allocate 10GB THPs and mlock them (so some THPs are allocated in the CMA region and mlocked), reserving 6 1GB hugetlb pages via /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages will get stuck (looping in too_many_isolated function) until we kill either task. With the patch applied, oom will kill the application with 10GB THPs and let hugetlb page reservation finish.
Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) Signed-off-by: Zi Yan ziy@nvidia.com Reviewed-by: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org
Acked-by: Vlastimil Babka vbabka@suse.cz
mm/compaction.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c index ee1f8439369e..3e834ac402f1 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, isolate_success: list_add(&page->lru, &cc->migratepages);
cc->nr_migratepages++;nr_isolated++;
cc->nr_migratepages += compound_nr(page);nr_isolated += compound_nr(page);/* * Avoid isolating too much unless this block is being @@ -1021,7 +1021,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, * or a lock is contended. For contention, isolate quickly to * potentially remove one source of contention. */
if (cc->nr_migratepages == COMPACT_CLUSTER_MAX &&
if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&@@ -1132,7 +1132,7 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, if (!pfn) break;
if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX) break;
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