From: Zi Yan ziy@nvidia.com
next inclusion from next-20240510 commit 7262f208ca681385d133844be8a58d9b4ca185f7 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9OCYO CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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If the source folio is on deferred split list, it is likely some subpages are not used. Split it before migration to avoid migrating unused subpages.
Commit 616b8371539a6 ("mm: thp: enable thp migration in generic path") did not check if a THP is on deferred split list before migration, thus, the destination THP is never put on deferred split list even if the source THP might be. The opportunity of reclaiming free pages in a partially mapped THP during deferred list scanning is lost, but no other harmful consequence is present[1].
[1]: https://lore.kernel.org/linux-mm/03CE3A00-917C-48CC-8E1C-6A98713C817C@nvidia...
[zi.yan@sent.com: fix an error in migrate_misplaced_folio()] Link: https://lkml.kernel.org/r/20240326150031.569387-1-zi.yan@sent.com Link: https://lkml.kernel.org/r/20240322193304.522496-1-zi.yan@sent.com Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path") Signed-off-by: Zi Yan ziy@nvidia.com Tested-by: Baolin Wang baolin.wang@linux.alibaba.com Reviewed-by: Baolin Wang baolin.wang@linux.alibaba.com Acked-by: David Hildenbrand david@redhat.com Cc: Huang, Ying ying.huang@intel.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Ryan Roberts ryan.roberts@arm.com Cc: SeongJae Park sj@kernel.org Cc: Yang Shi shy828301@gmail.com Cc: Yin Fengwei fengwei.yin@intel.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com --- mm/migrate.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
diff --git a/mm/migrate.c b/mm/migrate.c index cd2a24c6a745..936ed28f90c8 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1653,6 +1653,29 @@ static int migrate_pages_batch(struct list_head *from,
cond_resched();
+ /* + * The rare folio on the deferred split list should + * be split now. It should not count as a failure. + * Only check it without removing it from the list. + * Since the folio can be on deferred_split_scan() + * local list and removing it can cause the local list + * corruption. Folio split process below can handle it + * with the help of folio_ref_freeze(). + * + * nr_pages > 2 is needed to avoid checking order-1 + * page cache folios. They exist, in contrast to + * non-existent order-1 anonymous folios, and do not + * use _deferred_list. + */ + if (nr_pages > 2 && + !list_empty(&folio->_deferred_list)) { + if (try_split_folio(folio, split_folios) == 0) { + stats->nr_thp_split += is_thp; + stats->nr_split++; + continue; + } + } + /* * Large folio migration might be unsupported or * the allocation might be failed so we should retry