On Wed, May 26, 2021 at 12:27 AM Roman Gushchin <guro@xxxxxx> wrote: > > On Wed, Apr 21, 2021 at 03:00:48PM +0800, Muchun Song wrote: > > Because memory allocations pinning memcgs for a long time - it exists > > at a larger scale and is causing recurring problems in the real world: > > page cache doesn't get reclaimed for a long time, or is used by the > > second, third, fourth, ... instance of the same job that was restarted > > into a new cgroup every time. Unreclaimable dying cgroups pile up, > > waste memory, and make page reclaim very inefficient. > > > > We can convert LRU pages and most other raw memcg pins to the objcg > > direction to fix this problem, and then the page->memcg will always > > point to an object cgroup pointer. > > > > Therefore, the infrastructure of objcg no longer only serves > > CONFIG_MEMCG_KMEM. In this patch, we move the infrastructure of the > > objcg out of the scope of the CONFIG_MEMCG_KMEM so that the LRU pages > > can reuse it to charge pages. > > > > We know that the LRU pages are not accounted at the root level. But > > the page->memcg_data points to the root_mem_cgroup. So the > > page->memcg_data of the LRU pages always points to a valid pointer. > > But the root_mem_cgroup dose not have an object cgroup. If we use > > obj_cgroup APIs to charge the LRU pages, we should set the > > page->memcg_data to a root object cgroup. So we also allocate an > > object cgroup for the root_mem_cgroup. > > Overall the patch looks very good to me. There are few small things to enhance: > > 1) I'd rename it. Looking at the title I expect a trivial code move, > however the patch is doing more than this: e.g. allocating an objcg > for the root memcg. Something like "prepare objcg API for non-kmem usage". OK. I will rename it. > 2) How about obj_cgroup_release_kmem() instead of obj_cgroup_release_uncharge()? LGTM. Will use this name. > 3) The first paragraph of the commit log looks a bit vague: which allocations > pinning memcgs? How about something like this? > > Pagecache pages are charged at the allocation time and holding a reference > to the original memory cgroup until being reclaimed. Depending on the memory > pressure, specific patterns of the page sharing between different cgroups and > the cgroup creation and destruction rates, a large number of dying memory > cgroups can be pinned by pagecache pages. It makes the page reclaim less > efficient and wastes memory. More clear. I would love to use this. Thanks Roman. > > > Thanks!
