From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 2 Apr 2007 23:09:54 -0700 From: Andrew Morton Subject: Re: [PATCH] Cleanup and kernelify shrinker registration (rc5-mm2) Message-Id: <20070402230954.27840721.akpm@linux-foundation.org> In-Reply-To: <1175579225.12230.504.camel@localhost.localdomain> References: <1175571885.12230.473.camel@localhost.localdomain> <20070402205825.12190e52.akpm@linux-foundation.org> <1175575503.12230.484.camel@localhost.localdomain> <20070402215702.6e3782a9.akpm@linux-foundation.org> <1175579225.12230.504.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rusty Russell Cc: lkml - Kernel Mailing List , linux-mm@kvack.org, xfs-masters@oss.sgi.com, reiserfs-dev@namesys.com List-ID: On Tue, 03 Apr 2007 15:47:05 +1000 Rusty Russell wrote: > On Mon, 2007-04-02 at 21:57 -0700, Andrew Morton wrote: > > On Tue, 03 Apr 2007 14:45:02 +1000 Rusty Russell wrote: > > > Does that mean the to function correctly every user needs some internal > > > cursor so it doesn't end up scanning the first N entries over and over? > > > > > > > If it wants to be well-behaved, and to behave as the VM expects, yes. > > > > There's an expectation that the callback will be performing some scan-based > > aging operation and of course to do LRU (or whatever) aging, the callback > > will need to remember where it was up to last time it was called. > > > > But it's just a guideline - callbacks could do something different but > > in-the-spirit, I guess. > > Hmm, actually the callers I looked at (nfs, dcache, mbcache) seem to use > an LRU list and just walk the first "nr_to_scan" entries, and nr_to_scan > is always 128. That's just because of the batching logic up in shrink_slab(). And iirc we only break the scanning into lumps of 128 items so we can add a cond_resched() into it. > Someone who keeps a cursor will be disadvantaged: the other shrinkers > could well get less effective on repeated calls, but we won't. Someone > who picks entries at random might have the same issue. To examine the balancing one would need to examine the value of total_scan in shrink_slab(), rather than looking at the value which shrink_slab() passes into the callback. > I think it is clearest to describe how we expect everyone to work, and > let whoever is getting creative worry about it themselves. > > How's this: > == > Cleanup and kernelify shrinker registration. hm, well, six-of-one, VI of the other. We save maybe four kmallocs across the entire uptime at the cost of exposing stuff kernel-side which doesn't need to be exposed. But I think we need to weed that crappiness out of XFS first. -- 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