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[217.140.101.70]) by mx.google.com with ESMTP id f25si1271660ejf.32.2019.03.28.03.30.26 for ; Thu, 28 Mar 2019 03:30:27 -0700 (PDT) Received-SPF: pass (google.com: domain of catalin.marinas@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: domain of catalin.marinas@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=catalin.marinas@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 16F7F15AB; Thu, 28 Mar 2019 03:30:26 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 03B863F59C; Thu, 28 Mar 2019 03:30:23 -0700 (PDT) Date: Thu, 28 Mar 2019 10:30:21 +0000 From: Catalin Marinas To: Pekka Enberg Cc: Qian Cai , akpm@linux-foundation.org, cl@linux.com, mhocko@kernel.org, willy@infradead.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation Message-ID: <20190328103020.GA10283@arrakis.emea.arm.com> References: <20190327005948.24263-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Thu, Mar 28, 2019 at 08:05:31AM +0200, Pekka Enberg wrote: > On 27/03/2019 2.59, 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. > > Unfortunately I am not that brave soul, but I'm wondering what the > complication here is? It shouldn't be too hard to teach calculate_sizes() in > SLUB about a new SLAB_KMEMLEAK flag that reserves spaces for the metadata. I don't think it's the calculate_sizes() that's the hard part. The way kmemleak is designed assumes that the metadata has a longer lifespan than the slab object it is tracking (and refcounted via get_object/put_object()). We'd have to replace some of the rcu_read_(un)lock() regions with a full kmemleak_lock together with a few more tweaks to allow the release of kmemleak_lock during memory scanning (which can take minutes; so it needs to be safe w.r.t. metadata freeing, currently relying on a deferred RCU freeing). Anyway, I think it is possible, just not straight forward. -- Catalin