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Subject[PATCH] mm, thp: Do not queue fully unmapped pages for deferred split
Date
Adding fully unmapped pages into deferred split queue is not productive:
these pages are about to be freed or they are pinned and cannot be split
anyway.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/rmap.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 003377e24232..45388f1bf317 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
if (TestClearPageDoubleMap(page)) {
/*
* Subpages can be mapped with PTEs too. Check how many of
- * themi are still mapped.
+ * them are still mapped.
*/
for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
if (atomic_add_negative(-1, &page[i]._mapcount))
nr++;
}
+
+ /*
+ * Queue the page for deferred split if at least one small
+ * page of the compound page is unmapped, but at least one
+ * small page is still mapped.
+ */
+ if (nr && nr < HPAGE_PMD_NR)
+ deferred_split_huge_page(page);
} else {
nr = HPAGE_PMD_NR;
}
@@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
if (unlikely(PageMlocked(page)))
clear_page_mlock(page);

- if (nr) {
+ if (nr)
__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
- deferred_split_huge_page(page);
- }
}

/**
--
2.21.0
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