+ mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails.patch added to -mm tree

+ mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm, slub: consider rest of partial list if acquire_slab() fails
has been added to the -mm tree.  Its filename is
     mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails.patch

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------------------------------------------------------
From: Jann Horn <jannh@google.com>
Subject: mm, slub: consider rest of partial list if acquire_slab() fails

acquire_slab() fails if there is contention on the freelist of the page
(probably because some other CPU is concurrently freeing an object from
the page).  In that case, it might make sense to look for a different page
(since there might be more remote frees to the page from other CPUs, and
we don't want contention on struct page).

However, the current code accidentally stops looking at the partial list
completely in that case.  Especially on kernels without CONFIG_NUMA set,
this means that get_partial() fails and new_slab_objects() falls back to
new_slab(), allocating new pages.  This could lead to an unnecessary
increase in memory fragmentation.

Link: https://lkml.kernel.org/r/20201228130853.1871516-1-jannh@google.com
Fixes: 7ced37197196 ("slub: Acquire_slab() avoid loop")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/slub.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/slub.c~mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails
+++ a/mm/slub.c
@@ -1973,7 +1973,7 @@ static void *get_partial_node(struct kme
 
 		t = acquire_slab(s, n, page, object == NULL, &objects);
 		if (!t)
-			break;
+			continue; /* cmpxchg raced */
 
 		available += objects;
 		if (!object) {
_

Patches currently in -mm which might be from jannh@google.com are

mm-slub-consider-rest-of-partial-list-if-acquire_slab-fails.patch