From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH 1/5] inode: Make unused inode LRU per superblock Date: Thu, 27 May 2010 12:04:45 +1000 Message-ID: <20100527020445.GF22536@laptop> References: <1274777588-21494-1-git-send-email-david@fromorbit.com> <1274777588-21494-2-git-send-email-david@fromorbit.com> <20100526161732.GC22536@laptop> <20100526230129.GA1395@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, xfs@oss.sgi.com To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <20100526230129.GA1395@dastard> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, May 27, 2010 at 09:01:29AM +1000, Dave Chinner wrote: > On Thu, May 27, 2010 at 02:17:33AM +1000, Nick Piggin wrote: > > On Tue, May 25, 2010 at 06:53:04PM +1000, Dave Chinner wrote: > > > From: Dave Chinner > > >=20 > > > The inode unused list is currently a global LRU. This does not matc= h > > > the other global filesystem cache - the dentry cache - which uses > > > per-superblock LRU lists. Hence we have related filesystem object > > > types using different LRU reclaimatin schemes. > >=20 > > Is this an improvement I wonder? The dcache is using per sb lists > > because it specifically requires sb traversal. >=20 > Right - I originally implemented the per-sb dentry lists for > scalability purposes. i.e. to avoid monopolising the dentry_lock > during unmount looking for dentries on a specific sb and hanging the > system for several minutes. >=20 > However, the reason for doing this to the inode cache is not for > scalability, it's because we have a tight relationship between the > dentry and inode cache=D1=95. That is, reclaim from the dentry LRU grow= s > the inode LRU. Like the registration of the shrinkers, this is kind > of an implicit, undocumented behavour of the current shrinker > implemenation. Right, that's why I wonder whether it is an improvement. It would be interesting to see some tests (showing at least parity). =20 > What this patch series does is take that implicit relationship and > make it explicit. It also allows other filesystem caches to tie > into the relationship if they need to (e.g. the XFS inode cache). > What it _doesn't do_ is change the macro level behaviour of the > shrinkers... >=20 > > What allocation/reclaim really wants (for good scalability and NUMA > > characteristics) is per-zone lists for these things. It's easy to > > convert a single list into per-zone lists. > > > > It is much harder to convert per-sb lists into per-sb x per-zone list= s. >=20 > No it's not. Just convert the s_{dentry,inode}_lru lists on each > superblock and call the shrinker with a new zone mask field to pick > the correct LRU. That's no harder than converting a global LRU. > Anyway, you'd still have to do per-sb x per-zone lists for the dentry L= RUs, > so changing the inode cache to per-sb makes no difference. Right, it just makes it harder to do. By much harder, I did mostly mean the extra memory overhead. If there is *no* benefit from doing per-sb icache then I would question whether we should. =20 > However, this is a moot point because we don't have per-zone shrinker > interfaces. That's an entirely separate discussion because of the > macro-level behavioural changes it implies.... Yep. I have some patches for it, but they're currently behind the other fine grained locking stuff. But it's something that really needs to be implemented, IMO. -- 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