From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f173.google.com (mail-we0-f173.google.com [74.125.82.173]) by kanga.kvack.org (Postfix) with ESMTP id 1A4216B006E for ; Wed, 18 Mar 2015 10:38:56 -0400 (EDT) Received: by wetk59 with SMTP id k59so33989217wet.3 for ; Wed, 18 Mar 2015 07:38:55 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id t1si3882950wiv.116.2015.03.18.07.38.54 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 18 Mar 2015 07:38:54 -0700 (PDT) Date: Wed, 18 Mar 2015 14:38:47 +0000 From: Mel Gorman Subject: Re: [PATCH] mm: Use GFP_KERNEL allocation for the page cache in page_cache_read Message-ID: <20150318143847.GC3087@suse.de> References: <1426687766-518-1-git-send-email-mhocko@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1426687766-518-1-git-send-email-mhocko@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Al Viro , Johannes Weiner , Rik van Riel , Neil Brown , Tetsuo Handa , Sage Weil , Mark Fasheh , linux-mm@kvack.org, LKML On Wed, Mar 18, 2015 at 03:09:26PM +0100, 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 so it doesn't need this > protection. Even ceph and ocfs2 which call filemap_fault from their > fault handlers seem to be OK because they are not taking any fs lock > before invoking generic implementation. > > The protection might be even harmful. There is a strong push to fail > GFP_NOFS allocations rather than loop within allocator indefinitely with > a very limited reclaim ability. Once we start failing those requests > the OOM killer might be triggered prematurely because the page cache > allocation failure is propagated up the page fault path and end up in > pagefault_out_of_memory. > > Use GFP_KERNEL mask instead because it is safe from the reclaim > recursion POV. We are already doing GFP_KERNEL allocations down > add_to_page_cache_lru path. > > Reported-by: Tetsuo Handa > Signed-off-by: Michal Hocko I'm very far behind after LSF/MM so do not know where this came out of but it loses addressing restriction hints from the driver such as drivers/gpu/drm/gma500/gem.c: mapping_set_gfp_mask(r->gem.filp->f_mapping, GFP_KERNEL | __GFP_DMA32); It also loses mobility hints for fragmentation avoidance. fs/inode.c: mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE); If users of mapping_set_gfp_mask are now being ignored then it should at least trigger a once-off warning that the flags are being ignored so it's obvious if a recursion does occur and cause problems. -- Mel Gorman 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