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mm: migrate: check mapcount for THP instead of refcount

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The generic migration path will check refcount, so no need check refcount
here.  But the old code actually prevents from migrating shared THP
(mapped by multiple processes), so bail out early if mapcount is > 1 to
keep the behavior.

Link: https://lkml.kernel.org/r/20210518200801.7413-7-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Yang Shi 2021-06-30 18:51:51 -07:00 committed by Linus Torvalds
parent b0b515bfb3
commit 662aeea753
1 changed files with 4 additions and 12 deletions
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16
mm/migrate.c
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@ -2073,6 +2073,10 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
/* Do not migrate THP mapped by multiple processes */
if (PageTransHuge(page) && total_mapcount(page) > 1)
return 0;
/* Avoid migrating to a node that is nearly full */
if (!migrate_balanced_pgdat(pgdat, compound_nr(page)))
return 0;
@ -2080,18 +2084,6 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
if (isolate_lru_page(page))
return 0;
/*
* migrate_misplaced_transhuge_page() skips page migration's usual
* check on page_count(), so we must do it here, now that the page
* has been isolated: a GUP pin, or any other pin, prevents migration.
* The expected page count is 3: 1 for page's mapcount and 1 for the
* caller's pin and 1 for the reference taken by isolate_lru_page().
*/
if (PageTransHuge(page) && page_count(page) != 3) {
putback_lru_page(page);
return 0;
}
page_lru = page_is_file_lru(page);
mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru,
thp_nr_pages(page));