From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4184FC43387 for ; Mon, 17 Dec 2018 14:49:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F6C72133F for ; Mon, 17 Dec 2018 14:49:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1545058153; bh=TUaH+jb/o3KpAYoxtRRzjueo2P22RXq8n/bgDIeuaNg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=K0N4q5BKs5qpgXy3BbRJhyLt9J+aysbEYQj11t/CakiDyIrHYtdcN+r+6fD/FPfgT nudDa1yp7ckF+C8EsZDrpdGV/kOjsJWs1vlYRLDxs6lpBysMLQmK1oYHcxIdTtvFzS N4I81/VN5pzhM5W+sD4tOennDwlUEdcdX82gbJn0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733149AbeLQOtM (ORCPT ); Mon, 17 Dec 2018 09:49:12 -0500 Received: from mx2.suse.de ([195.135.220.15]:54086 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732489AbeLQOtK (ORCPT ); Mon, 17 Dec 2018 09:49:10 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id AF0EAAC90; Mon, 17 Dec 2018 14:49:08 +0000 (UTC) Date: Mon, 17 Dec 2018 15:49:08 +0100 From: Michal Hocko To: Matthew Wilcox Cc: Tetsuo Handa , Hou Tao , phillip@squashfs.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang in mem alloc Message-ID: <20181217144908.GQ30879@dhcp22.suse.cz> References: <20181204020840.49576-1-houtao1@huawei.com> <20181215143824.GJ10600@bombadil.infradead.org> <69457a5a-79c9-4950-37ae-eff7fa4f949a@huawei.com> <20181217035157.GK10600@bombadil.infradead.org> <20181217093337.GC30879@dhcp22.suse.cz> <00ff5d2d-a50f-4730-db8a-cea3d7a3eef7@I-love.SAKURA.ne.jp> <20181217122546.GL10600@bombadil.infradead.org> <20181217141044.GP30879@dhcp22.suse.cz> <20181217144101.GN10600@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181217144101.GN10600@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 17-12-18 06:41:01, Matthew Wilcox wrote: > On Mon, Dec 17, 2018 at 03:10:44PM +0100, Michal Hocko wrote: > > On Mon 17-12-18 04:25:46, Matthew Wilcox wrote: > > > It's worth noticing that squashfs _is_ in fact holding a page locked in > > > squashfs_copy_cache() when it calls grab_cache_page_nowait(). I'm not > > > sure if this will lead to trouble or not because I'm insufficiently > > > familiar with the reclaim path. > > > > Hmm, this is more interesting then. If there is any memcg accounted > > allocation down that path _and_ the squashfs writeout can lock more > > pages and mark them writeback before they are really sent to the storage > > then we have a problem. See [1] > > > > [1] http://lkml.kernel.org/r/20181213092221.27270-1-mhocko@kernel.org > > Squashfs is read only, so it'll never have dirty pages and never do > writeout. > > But ... maybe the GFP flags being used for grab_cache_page_nowait() are > wrong. It does, after all, say "nowait". Perhaps it shouldn't be trying > direct reclaim at all, but rather fail earlier. Like this: > > +++ b/mm/filemap.c > @@ -1550,6 +1550,8 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > gfp_mask |= __GFP_WRITE; > if (fgp_flags & FGP_NOFS) > gfp_mask &= ~__GFP_FS; > + if (fgp_flags & FGP_NOWAIT) > + gfp_mask &= ~__GFP_DIRECT_RECLAIM; > > page = __page_cache_alloc(gfp_mask); > if (!page) Isn't FGP_NOWAIT about page lock rather than the allocation context? -- Michal Hocko SUSE Labs