From mboxrd@z Thu Jan 1 00:00:00 1970 From: Trond Myklebust Subject: Re: [PATCH] NFS: Use GFP_NOFS in nfs_direct_req_alloc Date: Tue, 08 Sep 2009 23:49:53 -0400 Message-ID: <1252468193.5092.29.camel@heimdal.trondhjem.org> References: <20090908220230.7590.69833.stgit@matisse.1015granger.net> <1252449178.8099.64.camel@heimdal.trondhjem.org> <931F30AB-DC64-4A02-A96C-FABF0DD4059A@oracle.com> <1252451130.8099.81.camel@heimdal.trondhjem.org> <91BC2823-945F-4E23-A3E1-3CE1456C05DC@oracle.com> <1252460233.5092.12.camel@heimdal.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-nfs@vger.kernel.org To: Chuck Lever Return-path: Received: from mx2.netapp.com ([216.240.18.37]:64232 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751627AbZIIDu2 (ORCPT ); Tue, 8 Sep 2009 23:50:28 -0400 In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, 2009-09-08 at 22:16 -0400, Chuck Lever wrote: > On Sep 8, 2009, at 9:37 PM, Trond Myklebust wrote: > > On Tue, 2009-09-08 at 21:01 -0400, Chuck Lever wrote: > >> That is precisely the case here, in fact. The upper file system is > >> attempting to reclaim memory in the same kernel where the NFS client > >> is trying to allocate with GFP_KERNEL. > > > > That's the "upper file system"'s problem, not ours... Stacking > > filesystems causes issues. Screwing over the existing users of the > > underlying filesystem is not a fix for those issues... > > How does this change "screw over" the existing users of NFS O_DIRECT? If they are low on memory, and call read() or write() on an O_DIRECT file, the kernel will fail to start the necessary memory reclaim. Given that by far the most common users of NFS O_DIRECT these days tend to be large databases with rather heavy memory requirements our code changes should rather be moving in the opposite direction w.r.t. use of GFP_NOFS. -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@netapp.com www.netapp.com