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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: e87b0942-1915-4fbd-e157-08d686f7a820 X-MS-Exchange-CrossTenant-originalarrivaltime: 30 Jan 2019 21:12:34.4907 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2230 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-30_16:,, signatures=0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 29, 2019 at 02:15:25PM -0500, Chris Down wrote: > Roman points out that when when we do the low reclaim pass, we scale the > reclaim pressure relative to position between 0 and the maximum > protection threshold. >=20 > However, if the maximum protection is based on memory.elow, and > memory.emin is above zero, this means we still may get binary behaviour > on second-pass low reclaim. This is because we scale starting at 0, not > starting at memory.emin, and since we don't scan at all below emin, we > end up with cliff behaviour. >=20 > This should be a fairly uncommon case since usually we don't go into the > second pass, but it makes sense to scale our low reclaim pressure > starting at emin. >=20 > You can test this by catting two large sparse files, one in a cgroup > with emin set to some moderate size compared to physical RAM, and > another cgroup without any emin. In both cgroups, set an elow larger > than 50% of physical RAM. The one with emin will have less page > scanning, as reclaim pressure is lower. >=20 > Signed-off-by: Chris Down > Suggested-by: Roman Gushchin > Cc: Johannes Weiner > Cc: Andrew Morton > Cc: Michal Hocko > Cc: Tejun Heo > Cc: Roman Gushchin > Cc: Dennis Zhou > Cc: linux-kernel@vger.kernel.org > Cc: cgroups@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: kernel-team@fb.com Acked-by: Roman Gushchin Thanks!