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[195.135.220.15]) by mx.google.com with ESMTPS id m12si13588287edm.38.2019.07.16.13.07.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Jul 2019 13:07:17 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org 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 AF0E5ABE3; Tue, 16 Jul 2019 20:07:16 +0000 (UTC) Date: Tue, 16 Jul 2019 22:07:15 +0200 From: Michal Hocko To: Qian Cai Cc: Yang Shi , catalin.marinas@arm.com, dvyukov@google.com, rientjes@google.com, willy@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Revert "kmemleak: allow to coexist with fault injection" Message-ID: <20190716200715.GA14663@dhcp22.suse.cz> References: <1563299431-111710-1-git-send-email-yang.shi@linux.alibaba.com> <1563301410.4610.8.camel@lca.pw> <1563304877.4610.10.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1563304877.4610.10.camel@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 16-07-19 15:21:17, Qian Cai wrote: [...] > Thanks to this commit, there are allocation with __GFP_DIRECT_RECLAIM that > succeeded would keep trying with __GFP_NOFAIL for kmemleak tracking object > allocations. Well, not really. Because low order allocations with __GFP_DIRECT_RECLAIM basically never fail (they keep retrying) even without GFP_NOFAIL because that flag is actually to guarantee no failure. And for high order allocations the nofail mode is actively harmful. It completely changes the behavior of a system. A light costly order workload could put the system on knees and completely change the behavior. I am not really convinced this is a good behavior of a debugging feature TBH. > Otherwise, one kmemleak object allocation failure would kill the > whole kmemleak. Which is not great but quite likely a better than an unpredictable MM behavior caused by NOFAIL storms. Really, this NOFAIL patch is a completely broken behavior. There shouldn't be much discussion about reverting it. I would even argue it shouldn't have been merged in the first place. It doesn't have any acks nor reviewed-bys while it abuses __GFP_NOFAIL which is generally discouraged to be used. Thanks! -- Michal Hocko SUSE Labs