From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f179.google.com (mail-we0-f179.google.com [74.125.82.179]) by kanga.kvack.org (Postfix) with ESMTP id AA0726B0038 for ; Thu, 19 Mar 2015 08:44:45 -0400 (EDT) Received: by wetk59 with SMTP id k59so56239376wet.3 for ; Thu, 19 Mar 2015 05:44:45 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id eo8si2181478wjd.58.2015.03.19.05.44.43 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 19 Mar 2015 05:44:43 -0700 (PDT) Date: Thu, 19 Mar 2015 13:44:41 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: Use GFP_KERNEL allocation for the page cache in page_cache_read Message-ID: <20150319124441.GC12466@dhcp22.suse.cz> References: <1426687766-518-1-git-send-email-mhocko@suse.cz> <55098F3B.7070000@redhat.com> <20150318145528.GK17241@dhcp22.suse.cz> <20150319071439.GE28621@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150319071439.GE28621@dastard> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Chinner Cc: Rik van Riel , Andrew Morton , Al Viro , Johannes Weiner , Mel Gorman , Neil Brown , Tetsuo Handa , Sage Weil , Mark Fasheh , linux-mm@kvack.org, LKML On Thu 19-03-15 18:14:39, Dave Chinner wrote: > On Wed, Mar 18, 2015 at 03:55:28PM +0100, Michal Hocko wrote: > > On Wed 18-03-15 10:44:11, Rik van Riel wrote: > > > On 03/18/2015 10:09 AM, Michal Hocko wrote: > > > > page_cache_read has been historically using page_cache_alloc_cold to > > > > allocate a new page. This means that mapping_gfp_mask is used as the > > > > base for the gfp_mask. Many filesystems are setting this mask to > > > > GFP_NOFS to prevent from fs recursion issues. page_cache_read is, > > > > however, not called from the fs layer > > > > > > Is that true for filesystems that have directories in > > > the page cache? > > > > I haven't found any explicit callers of filemap_fault except for ocfs2 > > and ceph and those seem OK to me. Which filesystems you have in mind? > > Just about every major filesystem calls filemap_fault through the > .fault callout. That is right but the callback is called from the VM layer where we obviously do not take any fs locks (we are holding only mmap_sem for reading). Those who call filemap_fault directly (ocfs2 and ceph) and those who call the callback directly: qxl_ttm_fault, radeon_ttm_fault, kernfs_vma_fault, shm_fault seem to be safe from the reclaim recursion POV. radeon_ttm_fault takes a lock for reading but that one doesn't seem to be used from the reclaim context. Or did I miss your point? Are you concerned about some fs overloading filemap_fault and do some locking before delegating to filemap_fault? > C symbol: filemap_fault > > File Function Line > 0 9p/vfs_file.c 831 .fault = filemap_fault, > 1 9p/vfs_file.c 838 .fault = filemap_fault, > 2 btrfs/file.c 2081 .fault = filemap_fault, > 3 cifs/file.c 3242 .fault = filemap_fault, > 4 ext4/file.c 215 .fault = filemap_fault, > 5 f2fs/file.c 93 .fault = filemap_fault, > 6 fuse/file.c 2062 .fault = filemap_fault, > 7 gfs2/file.c 498 .fault = filemap_fault, > 8 nfs/file.c 653 .fault = filemap_fault, > 9 nilfs2/file.c 128 .fault = filemap_fault, > a ubifs/file.c 1536 .fault = filemap_fault, > b xfs/xfs_file.c 1420 .fault = filemap_fault, > > > > Btw. how would that work as we already have GFP_KERNEL allocation few > > lines below? > > GFP_KERNEL allocation for mappings is simply wrong. All mapping > allocations where the caller cannot pass a gfp_mask need to obey > the mapping_gfp_mask that is set by the mapping owner.... Hmm, I thought this is true only when the function might be called from the fs path. -- Michal Hocko SUSE Labs -- 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