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. Use thp_nr_pages to count pages. 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; }