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charset="us-ascii" Content-ID: <3094D3D488845C44BF820DA1A4FFFC13@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: cae3c621-689c-48ad-a9ae-08d6af1a4164 X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Mar 2019 23:01:02.4032 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB3089 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-22_13:,, signatures=0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe 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 Fri, Mar 22, 2019 at 10:49:46PM +0000, Chris Down wrote: > Roman Gushchin writes: > > I've noticed that the old version is just wrong: if cgroup_size is way = smaller > > than max(min, low), scan will be set to -lruvec_size. > > Given that it's unsigned long, we'll end up with scanning the whole lis= t > > (due to clamp() below). >=20 > Are you certain? If so, I don't see what you mean. This is how the code > looks in Linus' tree after the fixups: >=20 > unsigned long cgroup_size =3D mem_cgroup_size(memcg); > unsigned long baseline =3D 0; >=20 > if (!sc->memcg_low_reclaim) > baseline =3D lruvec_size; > scan =3D lruvec_size * cgroup_size / protection - baseline; >=20 > This works correctly as far as I can tell: I'm blaming the old version, not the new one. New one is perfectly fine, thanks to these lines: + /* Avoid TOCTOU with earlier protection check */ + cgroup_size =3D max(cgroup_size, protection); The old one was racy. Thanks!