Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751754AbbFANAW (ORCPT ); Mon, 1 Jun 2015 09:00:22 -0400 Received: from cantor2.suse.de ([195.135.220.15]:49095 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751973AbbFANAK (ORCPT ); Mon, 1 Jun 2015 09:00:10 -0400 From: Michal Hocko To: Cc: Andrew Morton , Dave Chinner , Neil Brown , Johannes Weiner , Al Viro , Mel Gorman , Rik van Riel , Tetsuo Handa , LKML , linux-fsdevel@vger.kernel.org Subject: [RFC 0/2] mapping_gfp_mask from the page fault path Date: Mon, 1 Jun 2015 15:00:01 +0200 Message-Id: <1433163603-13229-1-git-send-email-mhocko@suse.cz> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1590 Lines: 34 Hi, I somehow forgot about these patches. The previous version was posted here: http://marc.info/?l=linux-mm&m=142668784122763&w=2. The first attempt was broken but even when fixed it seems like ignoring mapping_gfp_mask in page_cache_read is too fragile because filesystems might use locks in their filemap_fault handlers which could trigger recursion problems as pointed out by Dave http://marc.info/?l=linux-mm&m=142682332032293&w=2. The first patch should be straightforward fix to obey mapping_gfp_mask when allocating for mapping. It can be applied even without the second one. The second patch is an attempt to handle mapping_gfp_mask from the page fault path properly. GFP_IOFS should be safe from he page fault path in general (we would be quite broken otherwise because there are places where GFP_KERNEL is used - e.g. pte allocation). MM will communicate this to the fs layer via struct vm_fault::gfp_mask. If fs needs to change this allocation context in a fs callback it can overwrite this mask. If the code flow gets back to MM we will obey this gfp_mask (e.g. in page_cache_read). This should be more appropriate than following mapping_gfp_mask blindly. See the patch description for more details. I am still not sure this is the right way to go so I am sending this as an RFC so any comments are highly appreciated. Thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/