From mboxrd@z Thu Jan 1 00:00:00 1970 In-reply-to: <1175684461.6483.64.camel@twins> (message from Peter Zijlstra on Wed, 04 Apr 2007 13:01:01 +0200) Subject: Re: [PATCH 6/6] mm: per device dirty threshold References: <20070403144047.073283598@taijtu.programming.kicks-ass.net> <20070403144224.709586192@taijtu.programming.kicks-ass.net> <1175681794.6483.43.camel@twins> <1175684461.6483.64.camel@twins> Message-Id: From: Miklos Szeredi Date: Wed, 04 Apr 2007 13:12:57 +0200 Sender: owner-linux-mm@kvack.org Return-Path: To: a.p.zijlstra@chello.nl Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, neilb@suse.de, dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com List-ID: > > > so it could be that: scale / cycle > 1 > > > by a very small amount; however: > > > > No, I'm worried about the case when scale is too small. If the > > per-bdi threshold becomes smaller than stat_threshold, then things > > won't work, because dirty+writeback will never go below the threshold, > > possibly resulting in the deadlock we are trying to avoid. > > /me goes refresh the deadlock details.. > > A writes to B; A exceeds the dirty limit but writeout is blocked by B > because the dirty limit is exceeded, right? > > This cannot happen when we decouple the BDI dirty thresholds, even when > a threshold is 0. > > A write to B; A exceeds A's limit and writes to B, B has limit of 0, the > 1 dirty page gets written out (we gain ratio) and life goes on. > > Right? If the limit is zero, then we need the per-bdi dirty+write to go to zero, otherwise balance_dirty_pages() loops. But the per-bdi writeback counter is not necessarily updated after the writeback, because the per-bdi per-CPU counter may not trip the update of the per-bdi counter. 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