On Wed, May 11, 2022 at 09:01:40AM +0300, Vasily Averin wrote: > 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. I don't think there is a better alternative than just having several set_active_memcg(parent);...set_active_memcg(old); places in the cgroup.c. Nesting is fine here, so it shouldn't be a big issue.
