mm: memcontrol: decouple reference counting from page accounting
The reference counting of a memcg is currently coupled directly to how many 4k pages are charged to it. This doesn't work well with Roman's new slab controller, which maintains pools of objects and doesn't want to keep an extra balance sheet for the pages backing those objects. This unusual refcounting design (reference counts usually track pointers to an object) is only for historical reasons: memcg used to not take any css references and simply stalled offlining until all charges had been reparented and the page counters had dropped to zero. When we got rid of the reparenting requirement, the simple mechanical translation was to take a reference for every charge. More historical context can be found in commit e8ea14cc ("mm: memcontrol: take a css reference for each charged page"), commit 64f21993 ("mm: memcontrol: remove obsolete kmemcg pinning tricks") and commit b2052564 ("mm: memcontrol: continue cache reclaim from offlined groups"). The new slab controller exposes the limitations in this scheme, so let's switch it to a more idiomatic reference counting model based on actual kernel pointers to the memcg: - The per-cpu stock holds a reference to the memcg its caching - User pages hold a reference for their page->mem_cgroup. Transparent huge pages will no longer acquire tail references in advance, we'll get them if needed during the split. - Kernel pages hold a reference for their page->mem_cgroup - Pages allocated in the root cgroup will acquire and release css references for simplicity. css_get() and css_put() optimize that. - The current memcg_charge_slab() already hacked around the per-charge references; this change gets rid of that as well. - tcp accounting will handle reference in mem_cgroup_sk_{alloc,free} Roman: 1) Rebased on top of the current mm tree: added css_get() in mem_cgroup_charge(), dropped mem_cgroup_try_charge() part 2) I've reformatted commit references in the commit log to make checkpatch.pl happy. [hughd@google.com: remove css_put_many() from __mem_cgroup_clear_mc()] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2007302011450.2347@eggly.anvilsSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org> Signed-off-by: NRoman Gushchin <guro@fb.com> Signed-off-by: NHugh Dickins <hughd@google.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Reviewed-by: NShakeel Butt <shakeelb@google.com> Acked-by: NRoman Gushchin <guro@fb.com> Acked-by: NMichal Hocko <mhocko@suse.com> Cc: Christoph Lameter <cl@linux.com> Cc: Tejun Heo <tj@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200623174037.3951353-6-guro@fb.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Showing
想要评论请 注册 或 登录