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authorHugh Dickins <hughd@google.com>2015-11-05 18:49:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-11-05 19:34:48 -0800
commit7db7671f835ccad66db20154ac1274140937d9b7 (patch)
treefce13f03cda6adf11e7be3cdab26ac7eb91a1145 /mm/migrate.c
parent2def7424c9be0069831380823fdb5cf72103b919 (diff)
downloadlinux-7db7671f835ccad66db20154ac1274140937d9b7.tar.bz2
mm: page migration trylock newpage at same level as oldpage
Clean up page migration a little by moving the trylock of newpage from move_to_new_page() into __unmap_and_move(), where the old page has been locked. Adjust unmap_and_move_huge_page() and balloon_page_migrate() accordingly. But make one kind-of-functional change on the way: whereas trylock of newpage used to BUG() if it failed, now simply return -EAGAIN if so. Cutting out BUG()s is good, right? But, to be honest, this is really to extend the usefulness of the custom put_new_page feature, allowing a pool of new pages to be shared perhaps with racing uses. Use an "else" instead of that "skip_unmap" label. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Christoph Lameter <cl@linux.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Rik van Riel <riel@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/migrate.c')
-rw-r--r--mm/migrate.c46
1 files changed, 26 insertions, 20 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 2f2e2236daf7..6d7774ef0e6c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -727,13 +727,8 @@ static int move_to_new_page(struct page *newpage, struct page *page,
struct address_space *mapping;
int rc;
- /*
- * Block others from accessing the page when we get around to
- * establishing additional references. We are the only one
- * holding a reference to the new page at this point.
- */
- if (!trylock_page(newpage))
- BUG();
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
/* Prepare mapping for the new page.*/
newpage->index = page->index;
@@ -774,9 +769,6 @@ static int move_to_new_page(struct page *newpage, struct page *page,
remove_migration_ptes(page, newpage);
page->mapping = NULL;
}
-
- unlock_page(newpage);
-
return rc;
}
@@ -861,6 +853,17 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
}
}
+ /*
+ * Block others from accessing the new page when we get around to
+ * establishing additional references. We are usually the only one
+ * holding a reference to newpage at this point. We used to have a BUG
+ * here if trylock_page(newpage) fails, but would like to allow for
+ * cases where there might be a race with the previous use of newpage.
+ * This is much like races on refcount of oldpage: just don't BUG().
+ */
+ if (unlikely(!trylock_page(newpage)))
+ goto out_unlock;
+
if (unlikely(isolated_balloon_page(page))) {
/*
* A ballooned page does not need any special attention from
@@ -870,7 +873,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
* the page migration right away (proteced by page lock).
*/
rc = balloon_page_migrate(newpage, page, mode);
- goto out_unlock;
+ goto out_unlock_both;
}
/*
@@ -889,30 +892,27 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
VM_BUG_ON_PAGE(PageAnon(page), page);
if (page_has_private(page)) {
try_to_free_buffers(page);
- goto out_unlock;
+ goto out_unlock_both;
}
- goto skip_unmap;
- }
-
- /* Establish migration ptes or remove ptes */
- if (page_mapped(page)) {
+ } else if (page_mapped(page)) {
+ /* Establish migration ptes */
try_to_unmap(page,
TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
page_was_mapped = 1;
}
-skip_unmap:
if (!page_mapped(page))
rc = move_to_new_page(newpage, page, page_was_mapped, mode);
if (rc && page_was_mapped)
remove_migration_ptes(page, page);
+out_unlock_both:
+ unlock_page(newpage);
+out_unlock:
/* Drop an anon_vma reference if we took one */
if (anon_vma)
put_anon_vma(anon_vma);
-
-out_unlock:
unlock_page(page);
out:
return rc;
@@ -1056,6 +1056,9 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
if (PageAnon(hpage))
anon_vma = page_get_anon_vma(hpage);
+ if (unlikely(!trylock_page(new_hpage)))
+ goto put_anon;
+
if (page_mapped(hpage)) {
try_to_unmap(hpage,
TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
@@ -1068,6 +1071,9 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
if (rc != MIGRATEPAGE_SUCCESS && page_was_mapped)
remove_migration_ptes(hpage, hpage);
+ unlock_page(new_hpage);
+
+put_anon:
if (anon_vma)
put_anon_vma(anon_vma);