linux-kernel - Re: [PATCH -mm v2 2/3] slub: fix kmem_cache

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Date:	Wed, 28 Jan 2015 20:46:39 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm v2 2/3] slub: fix kmem_cache_shrink return value

On Wed, Jan 28, 2015 at 10:33:50AM -0600, Christoph Lameter wrote:
> On Wed, 28 Jan 2015, Vladimir Davydov wrote:
> 
> > @@ -3419,6 +3420,9 @@ int __kmem_cache_shrink(struct kmem_cache *s)
> >  		for (i = SHRINK_PROMOTE_MAX - 1; i >= 0; i--)
> >  			list_splice_init(promote + i, &n->partial);
> >
> > +		if (n->nr_partial || slabs_node(s, node))
> 
> The total number of slabs obtained via slabs_node always contains the
> number of partial ones. So no need to check n->nr_partial.

Yeah, right. In addition to that I misplaced the check - it should go
after discard_slab, where we decrement nr_slabs. Here goes the updated
patch:

From: Vladimir Davydov <vdavydov@...allels.com>
Subject: [PATCH] slub: fix kmem_cache_shrink return value

It is supposed to return 0 if the cache has no remaining objects and 1
otherwise, while currently it always returns 0. Fix it.

Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
---
 mm/slub.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index dbf9334b6a5c..5626588db884 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3379,6 +3379,7 @@ int __kmem_cache_shrink(struct kmem_cache *s)
 	LIST_HEAD(discard);
 	struct list_head promote[SHRINK_PROMOTE_MAX];
 	unsigned long flags;
+	int ret = 0;
 
 	for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
 		INIT_LIST_HEAD(promote + i);
@@ -3424,9 +3425,12 @@ int __kmem_cache_shrink(struct kmem_cache *s)
 		/* Release empty slabs */
 		list_for_each_entry_safe(page, t, &discard, lru)
 			discard_slab(s, page);
+
+		if (slabs_node(s, node))
+			ret = 1;
 	}
 
-	return 0;
+	return ret;
 }
 
 static int slab_mem_going_offline_callback(void *arg)
-- 
1.7.10.4

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