Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752637AbXBSAzg (ORCPT ); Sun, 18 Feb 2007 19:55:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752638AbXBSAzg (ORCPT ); Sun, 18 Feb 2007 19:55:36 -0500 Received: from mail-gw2.sa.eol.hu ([212.108.200.109]:58991 "EHLO mail-gw2.sa.eol.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752637AbXBSAzf (ORCPT ); Sun, 18 Feb 2007 19:55:35 -0500 To: chris.mason@oracle.com CC: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org In-reply-to: <20070219004537.GB9289@think.oraclecorp.com> (message from Chris Mason on Sun, 18 Feb 2007 19:45:37 -0500) Subject: Re: dirty balancing deadlock References: <20070218125307.4103c04a.akpm@linux-foundation.org> <20070218145929.547c21c7.akpm@linux-foundation.org> <20070218155916.0d3c73a9.akpm@linux-foundation.org> <20070219004537.GB9289@think.oraclecorp.com> Message-Id: From: Miklos Szeredi Date: Mon, 19 Feb 2007 01:54:31 +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2211 Lines: 44 > > > > > If so, writes to B will decrease the dirty memory threshold. > > > > > > > > Yes, but not by enough. Say A dirties a 1100 pages, limit is 1000. > > > > Some pages queued for writeback (doesn't matter how much). B writes > > > > back 1, 1099 dirty remain in A, zero in B. balance_dirty_pages() for > > > > B doesn't know that there's nothing more to write back for B, it's > > > > just waiting there for those 1099, which'll never get written. > > > > > > hm, OK, arguable. I guess something like this.. > > > > Doesn't help the fuse case, but does seem to help the loopback mount > > one. > > > > For fuse it's worse with the patch: now the write triggered by the > > balance recurses into fuse, with disastrous results, since the fuse > > writeback is now blocked on the userspace queue. > > > > fusexmp_fh_no D 40136678 0 505 494 506 504 (NOTLB) > > 08982b78 00000001 00000000 08f9f9b4 0805d8cb 089a75f8 08982b78 08f98000 > > 08f98000 08f9f9dc 0805a38a 089a7100 08982680 08f9f9cc 08f98000 08f98000 > > 085d8300 08982680 089a7100 08f9fa34 08183006 089a7100 08982680 089a7100 Call Trace: > > 08f9f9a0: [<0805d8cb>] switch_to_skas+0x3b/0x83 > > 08f9f9b8: [<0805a38a>] _switch_to+0x49/0x99 > > 08f9f9e0: [<08183006>] schedule+0x246/0x547 > > 08f9fa38: [<08103c7e>] fuse_get_req_wp+0xe9/0x14a > > 08f9fa70: [<08103d2e>] fuse_writepage+0x4f/0x12c > > In general, writepage is supposed to do work without blocking on > expensive locks that will get pdflush and dirty reclaim stuck in this > fashion. You'll probably have to take the same approach reiserfs does > in data=journal mode, which is leaving the page dirty if fuse_get_req_wp > is going to block without making progress. Pdflush, and dirty reclaim set wbc->nonblocking to true. balance_dirty_pages and fsync don't. The problem here is that Andrew's patch is wrong to let balance_dirty_pages() try to write back pages from a different queue. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/