From mboxrd@z Thu Jan 1 00:00:00 1970 In-reply-to: <20070424045027.f21a79ae.akpm@linux-foundation.org> (message from Andrew Morton on Tue, 24 Apr 2007 04:50:27 -0700) Subject: Re: [PATCH 10/10] mm: per device dirty threshold References: <20070420155154.898600123@chello.nl> <20070420155503.608300342@chello.nl> <17965.29252.950216.971096@notabene.brown> <1177398589.26937.40.camel@twins> <1177403494.26937.59.camel@twins> <1177406817.26937.65.camel@twins> <20070424030021.a091018d.akpm@linux-foundation.org> <1177409538.26937.75.camel@twins> <20070424034024.f953f93f.akpm@linux-foundation.org> <20070424045027.f21a79ae.akpm@linux-foundation.org> Message-Id: From: Miklos Szeredi Date: Tue, 24 Apr 2007 14:07:21 +0200 Sender: owner-linux-mm@kvack.org Return-Path: To: akpm@linux-foundation.org Cc: miklos@szeredi.hu, a.p.zijlstra@chello.nl, neilb@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com, nikita@clusterfs.com, trond.myklebust@fys.uio.no, yingchao.zhou@gmail.com List-ID: > > No, we _start_ writeback for 1.5*ratelimit_pages pages, but do not > > wait for those writebacks to finish. > > > > So for a slow device and a fast writer, dirty+writeback can indeed > > increase beyond the dirty threshold. > > > > Nope, try it. > > If a process dirties 1000 pages it'll then go into balance_dirty_pages() > and start writeback against 1,500 pages. When we hit dirty_ratio that > process will be required to write back 1,500 pages for each eight pages > which it dirtied. We'll quickly reach the stage where there are no longer > 1,500 pages to be written back and the process will block in > balance_dirty_pages() until the dirty+writeback level subsides. OK. I was confused by this: static long ratelimit_pages = 32; and didn't realize, that that 32 is totally irrelevant. So I'm still right, that for N dirty pages, the writer is allowed to dirty N/1500*8 more dirty pages, but I agree, that this isn't really an issue. Miklos -- 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