From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755149Ab2GaPTm (ORCPT ); Tue, 31 Jul 2012 11:19:42 -0400 Received: from cantor2.suse.de ([195.135.220.15]:59658 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754955Ab2GaPTl (ORCPT ); Tue, 31 Jul 2012 11:19:41 -0400 Date: Tue, 31 Jul 2012 16:19:36 +0100 From: Mel Gorman To: "Myklebust, Trond" Cc: Stephen Rothwell , Andrew Morton , "linux-next@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Jeff Layton Subject: Re: linux-next: manual merge of the akpm tree with the nfs tree Message-ID: <20120731151936.GR612@suse.de> References: <20120731142441.0d01100f9d050ec6e479c923@canb.auug.org.au> <20120731103336.GN612@suse.de> <1343745442.519.20.camel@lade.trondhjem.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1343745442.519.20.camel@lade.trondhjem.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 31, 2012 at 02:37:24PM +0000, Myklebust, Trond wrote: > On Tue, 2012-07-31 at 11:33 +0100, Mel Gorman wrote: > > On Tue, Jul 31, 2012 at 02:24:41PM +1000, Stephen Rothwell wrote: > > > Hi Andrew, > > > > > > Today's linux-next merge of the akpm tree got a conflict in > > > net/sunrpc/xprtsock.c between commit 5cf02d09b50b ("nfs: skip commit in > > > releasepage if we're freeing memory for fs-related reasons") from the nfs > > > tree and commit "nfs: enable swap on NFS" from the akpm tree. > > > > > > Just context changes? I fixed it up (I think - see below) and can carry > > > the fix as necessary. > > > > Functionally it looks fine. As you say, it all looks like context > > changes. Arguably code like this > > > > current->flags &= ~PF_FSTRANS > > > > could use tsk_restore_flags instead() even though it should never be > > necessary as PF_FSTRANS would not be set on function entry. However, > > it would set up a depedency between the patch sets that is undesirable. > > If both sets get merged then it might make sense as a cleanup to use > > tsk_restore_flags() but not until then. > > > > Thanks Stephen. > > > > Do we really need to set both PF_FSTRANS and PF_MEMALLOC here? The > reason why I merged the PF_FSTRANS patch is that we have the deadlock > problem when allocating a new socket even before we add swap-over-nfs. > Adding PF_FSTRANS to disallow entry into the NFS layer by the memory > allocator fixes that issue. PF_FSTRANS is to prevent recursion into NFS and is set whether swap-over-NFS is used or not and for all requests. > What value does PF_MEMALLOC add? Is that in order to prevent recursion > into other areas of the swap code (say, if you mix swap-over-nfs with > ordinary swap-to-disk)? > PF_MEMALLOC is normally to prevent the page reclaim recursing into itself. Page reclaim can call the page allocator and that cannot re-enter page reclaim. In the case of swap-over-NFS, PF_MEMALLOC is set only if the socket is being used for swapping. In softirq context, the allocation request is allowed to use PFMEMALLOC reserves to avoid deadlock. I do not see an obvious way to collapse the two flags together. PF_FSTRANS should not mean the PFMEMALLOC reserves can be used and PFMEMALLOC is not set for all requests. -- Mel Gorman SUSE Labs