From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH -mm] fs: shrinker: always scan at least one object of each type Date: Tue, 13 Jan 2015 15:56:39 -0800 Message-ID: <20150113155639.53e48aad4b0cfe870ccffac4@linux-foundation.org> References: <1421058046-2434-1-git-send-email-vdavydov@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Johannes Weiner , Michal Hocko , Alexander Viro , , , To: Vladimir Davydov Return-path: In-Reply-To: <1421058046-2434-1-git-send-email-vdavydov@parallels.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Mon, 12 Jan 2015 13:20:46 +0300 Vladimir Davydov wrote: > In super_cache_scan() we divide the number of objects of particular type > by the total number of objects in order to distribute pressure among > different types of fs objects (inodes, dentries, fs-private objects). > As a result, in some corner cases we can get nr_to_scan=0 even if there > are some objects to reclaim, e.g. dentries=1, inodes=1, fs_objects=1, > nr_to_scan=1/3=0. > > This is unacceptable for per memcg kmem accounting, because this means > that some objects may never get reclaimed after memcg death, preventing > it from being freed. > > This patch therefore assures that super_cache_scan() will scan at least > one object of each type if any. > > --- a/fs/super.c > +++ b/fs/super.c > @@ -92,13 +92,13 @@ static unsigned long super_cache_scan(struct shrinker *shrink, > * prune the dcache first as the icache is pinned by it, then > * prune the icache, followed by the filesystem specific caches > */ > - sc->nr_to_scan = dentries; > + sc->nr_to_scan = dentries + 1; > freed = prune_dcache_sb(sb, sc); > - sc->nr_to_scan = inodes; > + sc->nr_to_scan = inodes + 1; > freed += prune_icache_sb(sb, sc); > > if (fs_objects) { > - sc->nr_to_scan = fs_objects; > + sc->nr_to_scan = fs_objects + 1; > freed += sb->s_op->free_cached_objects(sb, sc); > } A reader of this code will wonder "why is it adding 1 everywhere". Let's tell them? --- a/fs/super.c~fs-shrinker-always-scan-at-least-one-object-of-each-type-fix +++ a/fs/super.c @@ -91,6 +91,9 @@ static unsigned long super_cache_scan(st /* * prune the dcache first as the icache is pinned by it, then * prune the icache, followed by the filesystem specific caches + * + * Ensure that we always scan at least one object - memcg kmem + * accounting uses this to fully empty the caches. */ sc->nr_to_scan = dentries + 1; freed = prune_dcache_sb(sb, sc); _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org