From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx155.postini.com [74.125.245.155]) by kanga.kvack.org (Postfix) with SMTP id CB9CE6B0070 for ; Thu, 8 Nov 2012 14:21:22 -0500 (EST) Date: Thu, 8 Nov 2012 11:21:20 -0800 From: Andrew Morton Subject: Re: [PATCH v6 25/29] memcg/sl[au]b: shrink dead caches Message-Id: <20121108112120.fc964c29.akpm@linux-foundation.org> In-Reply-To: <0000013ae1050e6f-7f908e0b-720a-4e68-a275-e5086a4f5c74-000000@email.amazonses.com> References: <1351771665-11076-1-git-send-email-glommer@parallels.com> <1351771665-11076-26-git-send-email-glommer@parallels.com> <20121105164813.2eba5ecb.akpm@linux-foundation.org> <509A0A04.2030503@parallels.com> <20121106231627.3610c908.akpm@linux-foundation.org> <509A2849.9090509@parallels.com> <20121107144612.e822986f.akpm@linux-foundation.org> <0000013ae1050e6f-7f908e0b-720a-4e68-a275-e5086a4f5c74-000000@email.amazonses.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Glauber Costa , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, Johannes Weiner , Tejun Heo , Michal Hocko , Pekka Enberg , David Rientjes , Pekka Enberg , Suleiman Souhlal On Thu, 8 Nov 2012 17:15:36 +0000 Christoph Lameter wrote: > On Wed, 7 Nov 2012, Andrew Morton wrote: > > > What's up with kmem_cache_shrink? It's global and exported to modules > > but its only external caller is some weird and hopelessly poorly > > documented site down in drivers/acpi/osl.c. slab and slob implement > > kmem_cache_shrink() *only* for acpi! wtf? Let's work out what acpi is > > trying to actually do there, then do it properly, then killkillkill! > > kmem_cache_shrink is also used internally. Its simply releasing unused > cached objects. Only in slub. It could be removed outright from the others and simplified in slub. > > Secondly, as slab and slub (at least) have the ability to shed cached > > memory, why aren't they hooked into the core cache-shinking machinery. > > After all, it's called "shrink_slab"! > > Because the core cache shrinking needs the slab caches to free up memory > from inodes and dentries. We could call kmem_cache_shrink at the end of > the shrink passes in vmscan. The price would be that the caches would have > to be repopulated when new allocations occur. Well, the shrinker shouldn't strips away all the cache. It will perform a partial trim, the magnitude of which increases with perceived external memory pressure. AFACIT, this is correct and desirable behaviour for shrinking slab's internal caches. > > > > If we can fix all that up then I wonder whether this particular patch > > needs to exist at all. If the kmem_cache is no longer used then we > > can simply leave it floating around in memory and the regular cache > > shrinking code out of shrink_slab() will clean up any remaining pages. > > The kmem_cache itself can be reclaimed via another shrinker, if > > necessary? > > The kmem_cache can only be released if all its objects (used and unused) > are released. kmem_cache_shrink drops the unused objects on some internal > slab specific list. That may enable us to release the kmem_cache > structure. -- 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