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charset="us-ascii" Content-ID: <599C994690A61041AD935BB8453A9F22@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 70d1a8bd-6c31-4f76-45f6-08d75e13fbcf X-MS-Exchange-CrossTenant-originalarrivaltime: 31 Oct 2019 15:07:02.1197 (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-CrossTenant-userprincipalname: zKqY43CPRRpnob01h8AI2HObGd+OjfpX7b89fQJRHiGST00VZ5WVQA4WvcSLpsLg X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB2627 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,1.0.8 definitions=2019-10-31_06:2019-10-30,2019-10-31 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 suspectscore=0 phishscore=0 priorityscore=1501 adultscore=0 impostorscore=0 spamscore=0 lowpriorityscore=0 bulkscore=0 mlxlogscore=999 clxscore=1015 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1910310155 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 31, 2019 at 10:41:51AM -0400, Johannes Weiner wrote: > On Thu, Oct 31, 2019 at 01:52:44AM +0000, Roman Gushchin wrote: > > On Fri, Oct 25, 2019 at 03:41:18PM -0400, Johannes Weiner wrote: > > > @@ -3117,15 +3095,24 @@ void __memcg_kmem_uncharge(struct page *page,= int order) > > > css_put_many(&memcg->css, nr_pages); > > > } > > > =20 > > > -int __memcg_kmem_charge_subpage(struct mem_cgroup *memcg, size_t siz= e, > > > - gfp_t gfp) > > > +int obj_cgroup_charge(struct obj_cgroup *objcg, size_t size, gfp_t g= fp) > > > { > > > - return try_charge(memcg, gfp, size, true); > > > + int ret; > > > + > > > + if (consume_obj_stock(objcg, nr_bytes)) > > > + return 0; > > > + > > > + ret =3D try_charge(objcg->memcg, gfp, 1); > > > + if (ret) > > > + return ret; >=20 > > The second problem is also here. If a task belonging to a different mem= cg > > is scheduled on this cpu, most likely we will need to refill both stock= s, > > even if we need only a small temporarily allocation. >=20 > Yes, that's a good thing. The reason we have the per-cpu caches in the > first place is because most likely the same cgroup will perform > several allocations. Both the slab allocator and the page allocator > have per-cpu caches for the same reason. I don't really understand > what the argument is. I mean it seems strange (and most likely will show up in perf numbers) to move a page from one stock to another. Is there a reason why do you want to ask try_charge() and stock only a single page? Can we do the following instead? 1) add a boolean argument to try_charge() to bypass the consume_stock() cal= l at the beginning and just go slow path immediately 2) use try_charge() with this argument set to true to fill the objc/subpage stock with MEMCG_CHARGE_BATCH pages In this case we'll reuse try_charge() and will have all corresponding benef= its, but will avoid the double stocking, which seems as a strange idea to me. >=20 > > > + > > > + refill_obj_stock(objcg, PAGE_SIZE - size); > >=20 > > And the third problem is here. Percpu allocations (on which accounting = I'm > > working right now) can be larger than a page. >=20 > How about this? >=20 > nr_pages =3D round_up(size, PAGE_SIZE); > try_charge(objcg->memcg, nr_pages); > refill_obj_stock(objcg, size % PAGE_SIZE); Ok, this will work. >=20 > > This is fairly small issue in comparison to the first one. But it illus= trates > > well the main point: we can't simple get a page from the existing API a= nd > > sublease it in parts. The problem is that we need to break the main pri= nciple > > that a page belongs to a single memcg. >=20 > We can change the underlying assumptions of the existing API if they > are no longer correct. We don't have to invent a parallel stack. Ok, this makes sense. And thank you for the patch, I'll take it into the se= t. Thanks!