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=-7.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 0034CC43381 for ; Tue, 26 Mar 2019 16:34:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0B4F20863 for ; Tue, 26 Mar 2019 16:34:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553618042; bh=/HyRtG2JJ2e9eJTzDRtCjNBy/LXhKiM/DS1QmnVTQHw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=aL9eoEV56mRg34uAQjEHFsaRmrHvF/nUGmZlakCa8I2Uc+GBwrnkHVAFzpdXB2gpW KQxy3Du24lqTJIBnIJLue4eXvfaZjz6GMaODMmAxQwFA9frzxgfQYLexSD1k5iwFSe OEeM4CJdpCU/CqUjATCY1TGtBkM0S44LtVrJdFdM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731621AbfCZQeB (ORCPT ); Tue, 26 Mar 2019 12:34:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:43340 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726175AbfCZQeA (ORCPT ); Tue, 26 Mar 2019 12:34:00 -0400 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 9CD33ABC1; Tue, 26 Mar 2019 16:33:59 +0000 (UTC) Date: Tue, 26 Mar 2019 17:33:56 +0100 From: Michal Hocko To: Catalin Marinas Cc: Matthew Wilcox , Qian Cai , akpm@linux-foundation.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] kmemleaak: survive in a low-memory situation Message-ID: <20190326163356.GS28406@dhcp22.suse.cz> References: <20190326154338.20594-1-cai@lca.pw> <20190326160536.GO10344@bombadil.infradead.org> <20190326162038.GH33308@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190326162038.GH33308@arrakis.emea.arm.com> 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 Tue 26-03-19 16:20:41, Catalin Marinas wrote: > On Tue, Mar 26, 2019 at 09:05:36AM -0700, Matthew Wilcox wrote: > > On Tue, Mar 26, 2019 at 11:43:38AM -0400, Qian Cai wrote: > > > Unless there is a brave soul to reimplement the kmemleak to embed it's > > > metadata into the tracked memory itself in a foreseeable future, this > > > provides a good balance between enabling kmemleak in a low-memory > > > situation and not introducing too much hackiness into the existing > > > code for now. > > > > I don't understand kmemleak. Kirill pointed me at this a few days ago: > > > > https://gist.github.com/kiryl/3225e235fea390aa2e49bf625bbe83ec > > > > It's caused by the XArray allocating memory using GFP_NOWAIT | __GFP_NOWARN. > > kmemleak then decides it needs to allocate memory to track this memory. > > So it calls kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp)); > > > > #define gfp_kmemleak_mask(gfp) (((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \ > > __GFP_NORETRY | __GFP_NOMEMALLOC | \ > > __GFP_NOWARN | __GFP_NOFAIL) > > > > then the page allocator gets to see GFP_NOFAIL | GFP_NOWAIT and gets angry. > > > > But I don't understand why kmemleak needs to mess with the GFP flags at > > all. > > Originally, it was just preserving GFP_KERNEL | GFP_ATOMIC. Starting > with commit 6ae4bd1f0bc4 ("kmemleak: Allow kmemleak metadata allocations > to fail"), this mask changed, aimed at making kmemleak allocation > failures less verbose (i.e. just disable it since it's a debug tool). > > Commit d9570ee3bd1d ("kmemleak: allow to coexist with fault injection") > introduced __GFP_NOFAIL but this came with its own problems which have > been previously reported (the warning you mentioned is another one of > these). We didn't get to any clear conclusion on how best to allow > allocations to fail with fault injection but not for the kmemleak > metadata. Your suggestion below would probably do the trick. I have objected to that on several occasions. An implicit __GFP_NOFAIL is simply broken and __GFP_NOWAIT allocations are a shiny example of that. You cannot loop inside the allocator for an unbound amount of time potentially with locks held. I have heard that there are some plans to deal with that but nothing has really materialized AFAIK. d9570ee3bd1d should be reverted I believe. The proper way around is to keep a pool objects and keep spare objects for restrected allocation contexts. -- Michal Hocko SUSE Labs