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authorMatthew Wilcox (Oracle) <willy@infradead.org>2022-01-07 14:04:55 -0500
committerMatthew Wilcox (Oracle) <willy@infradead.org>2022-03-21 12:56:35 -0400
commit59409373f60a0a493fe2a1b85dc8c6299c4fef37 (patch)
tree359beb8af1ae79fce424d7a2cb6be59280d700dd /mm/gup.c
parent4c65422901154766e5cee17875ed680366a4a141 (diff)
mm/gup: Handle page split race more efficiently
If we hit the page split race, the current code returns NULL which will presumably trigger a retry under the mmap_lock. This isn't necessary; we can just retry the compound_head() lookup. This is a very minor optimisation of an unlikely path, but conceptually it matches (eg) the page cache RCU-protected lookup. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Diffstat (limited to 'mm/gup.c')
-rw-r--r--mm/gup.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/mm/gup.c b/mm/gup.c
index ad120f470735..d3e8266d8e70 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -68,7 +68,10 @@ static void put_page_refs(struct page *page, int refs)
*/
static inline struct page *try_get_compound_head(struct page *page, int refs)
{
- struct page *head = compound_head(page);
+ struct page *head;
+
+retry:
+ head = compound_head(page);
if (WARN_ON_ONCE(page_ref_count(head) < 0))
return NULL;
@@ -86,7 +89,7 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
*/
if (unlikely(compound_head(page) != head)) {
put_page_refs(head, refs);
- return NULL;
+ goto retry;
}
return head;