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[140.211.169.12]) by mx.google.com with ESMTPS id o6si36444112pfb.230.2019.07.30.13.39.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 Jul 2019 13:39:43 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from X1 (unknown [76.191.170.112]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id AB48A311D; Tue, 30 Jul 2019 20:39:40 +0000 (UTC) Date: Tue, 30 Jul 2019 13:39:39 -0700 From: Andrew Morton To: Qian Cai Cc: Catalin Marinas , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Matthew Wilcox Subject: Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak objects Message-Id: <20190730133939.2840b742408336e2a0a9f573@linux-foundation.org> In-Reply-To: <1564518157.11067.34.camel@lca.pw> References: <20190727132334.9184-1-catalin.marinas@arm.com> <20190730125743.113e59a9c449847d7f6ae7c3@linux-foundation.org> <1564518157.11067.34.camel@lca.pw> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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, 30 Jul 2019 16:22:37 -0400 Qian Cai wrote: > On Tue, 2019-07-30 at 12:57 -0700, Andrew Morton wrote: > > On Sat, 27 Jul 2019 14:23:33 +0100 Catalin Marinas > > wrote: > >=20 > > > Add mempool allocations for struct kmemleak_object and > > > kmemleak_scan_area as slightly more resilient than kmem_cache_alloc() > > > under memory pressure. Additionally, mask out all the gfp flags passed > > > to kmemleak other than GFP_KERNEL|GFP_ATOMIC. > > >=20 > > > A boot-time tuning parameter (kmemleak.mempool) is added to allow a > > > different minimum pool size (defaulting to NR_CPUS * 4). > >=20 > > Why would anyone ever want to alter this?=A0=A0Is there some particular > > misbehaviour which this will improve?=A0=A0If so, what is it? >=20 > So it can tolerant different systems and workloads. For example, there ar= e some > machines with slow disk and fast CPUs. When they are under memory pressur= e, it > could take a long time to swap before the OOM kicks in to free up some me= mory. > As the results, it needs a large mempool for kmemleak or suffering from h= igher > chance of a kmemleak metadata allocation failure. This sort of thing should be in the changelog and in the user-facing documentation please. Also, we should document the user-visible effects of this failure so that users can determine whether this tunable will help them.