From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932184Ab2DQMlG (ORCPT ); Tue, 17 Apr 2012 08:41:06 -0400 Received: from cantor2.suse.de ([195.135.220.15]:47521 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756072Ab2DQMlD (ORCPT ); Tue, 17 Apr 2012 08:41:03 -0400 Date: Tue, 17 Apr 2012 13:40:56 +0100 From: Mel Gorman To: Fred Isaman Cc: Andrew Morton , Linux-MM , Linux-Netdev , Linux-NFS , LKML , David Miller , Trond Myklebust , Neil Brown , Christoph Hellwig , Peter Zijlstra , Mike Christie , Eric B Munson Subject: Re: [PATCH 08/11] nfs: disable data cache revalidation for swapfiles Message-ID: <20120417124056.GI2359@suse.de> References: <1334578675-23445-1-git-send-email-mgorman@suse.de> <1334578675-23445-9-git-send-email-mgorman@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 Mon, Apr 16, 2012 at 9:44 AM, Mel Gorman wrote: > > On Mon, Apr 16, 2012 at 09:10:04AM -0400, Fred Isaman wrote: > >> > > >> > -static struct nfs_page *nfs_page_find_request_locked(struct page *page) > >> > +static struct nfs_page * > >> > +nfs_page_find_request_locked(struct nfs_inode *nfsi, struct page *page) > >> >  { > >> >        struct nfs_page *req = NULL; > >> > > >> > -       if (PagePrivate(page)) { > >> > +       if (PagePrivate(page)) > >> >                req = (struct nfs_page *)page_private(page); > >> > -               if (req != NULL) > >> > -                       kref_get(&req->wb_kref); > >> > +       else if (unlikely(PageSwapCache(page))) { > >> > +               struct nfs_page *freq, *t; > >> > + > >> > +               /* Linearly search the commit list for the correct req */ > >> > +               list_for_each_entry_safe(freq, t, &nfsi->commit_list, wb_list) { > >> > +                       if (freq->wb_page == page) { > >> > +                               req = freq; > >> > +                               break; > >> > +                       } > >> > +               } > >> > + > >> > +               BUG_ON(req == NULL); > >> > >> I suspect I am missing something, but why is it guaranteed that the > >> req is on the commit list? > >> > > > > It's a fair question and a statement about what I expected to happen. > > The commit list replaces the nfs_page_tree radix tree that used to exist > > and my understanding was that the req would exist in the radix tree until > > the swap IO was completed. I expected it to be the same for the commit > > list and the BUG_ON was based on that expectation. Are there cases where > > the req would not be found? > > > > A req is on the commit list only if it actually needs to be scheduled > for COMMIT. In other words, only after it has been sent via WRITE and > the server did not return NFS_FILE_SYNC. > > Thus dirtying a page, then trying to touch it again before the WRITE > is sent will not find the corresponding req on the commit_list. Thanks for the explanation. I'll remove the BUG_ON -- Mel Gorman SUSE Labs