On 5/11/22 06:06, Roman Gushchin wrote: > On Wed, May 04, 2022 at 12:00:18PM +0300, Vasily Averin wrote: >> From my point of view it is most important to account allocated memory >> to any cgroup inside container. Select of proper memcg is a secondary goal here. >> Frankly speaking I do not see a big difference between memcg of current process, >> memcg of newly created child and memcg of its parent. >> >> As far as I understand, Roman chose the parent memcg because it was a special >> case of creating a new memory group. He temporally changed active memcg >> in mem_cgroup_css_alloc() and properly accounted all required memcg-specific >> allocations. > > My primary goal was to apply the memory pressure on memory cgroups with a lot > of (dying) children cgroups. On a multi-cpu machine a memory cgroup structure > is way larger than a page, so a cgroup which looks small can be really large > if we calculate the amount of memory taken by all children memcg internals. > > Applying this pressure to another cgroup (e.g. the one which contains systemd) > doesn't help to reclaim any pages which are pinning the dying cgroups. > > For other controllers (maybe blkcg aside, idk) it shouldn't matter, because > there is no such problem there. > > For consistency reasons I'd suggest to charge all *large* allocations > (e.g. percpu) to the parent cgroup. Small allocations can be ignored. I showed in [1] other large allocation: " number bytes $1*$2 sum note call_site of alloc allocs ------------------------------------------------------------ 1 14448 14448 14448 = percpu_alloc_percpu: 1 8192 8192 22640 ++ (mem_cgroup_css_alloc+0x54) 49 128 6272 28912 ++ (__kernfs_new_node+0x4e) 49 96 4704 33616 ? (simple_xattr_alloc+0x2c) 49 88 4312 37928 ++ (__kernfs_iattrs+0x56) 1 4096 4096 42024 ++ (cgroup_mkdir+0xc7) 1 3840 3840 45864 = percpu_alloc_percpu: 4 512 2048 47912 + (alloc_fair_sched_group+0x166) 4 512 2048 49960 + (alloc_fair_sched_group+0x139) 1 2048 2048 52008 ++ (mem_cgroup_css_alloc+0x109) " [1] https://lore.kernel.org/all/1aa4cd22-fcb6-0e8d-a1c6-23661d618864@xxxxxxxxxx/ = already accounted ++ to be accounted first + to be accounted a bit later There is no problems with objects allocated in mem_cgroup_alloc(), they will be accounted to parent's memcg. However I do not understand how to handle other large objects? We could move set_active_memcg(parent) call from mem_cgroup_css_alloc() to cgroup_apply_control_enable() and handle allocation in all .css_alloc() However I need to handle allocations called from cgroup_mkdir() too and badly understand how to do it properly. Thank you, Vasily Averin
