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Date: Mon, 21 Sep 2020 10:12:00 +0200 From: Michal Hocko <mhocko@...e.com> To: zangchunxin@...edance.com Cc: hannes@...xchg.org, vdavydov.dev@...il.com, akpm@...ux-foundation.org, tj@...nel.org, lizefan@...wei.com, corbet@....net, ast@...nel.org, daniel@...earbox.net, kafai@...com, songliubraving@...com, yhs@...com, andriin@...com, john.fastabend@...il.com, kpsingh@...omium.org, cgroups@...r.kernel.org, linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, bpf@...r.kernel.org Subject: Re: [PATCH] mm/memcontrol: Add the drop_cache interface for cgroup v2 On Mon 21-09-20 16:02:55, zangchunxin@...edance.com wrote: > From: Chunxin Zang <zangchunxin@...edance.com> > > In the cgroup v1, we have 'force_mepty' interface. This is very > useful for userspace to actively release memory. But the cgroup > v2 does not. > > This patch reuse cgroup v1's function, but have a new name for > the interface. Because I think 'drop_cache' may be is easier to > understand :) This should really explain a usecase. Global drop_caches is a terrible interface and it has caused many problems in the past. People have learned to use it as a remedy to any problem they might see and cause other problems without realizing that. This is the reason why we even log each attempt to drop caches. I would rather not repeat the same mistake on the memcg level unless there is a very strong reason for it. > Signed-off-by: Chunxin Zang <zangchunxin@...edance.com> > --- > Documentation/admin-guide/cgroup-v2.rst | 11 +++++++++++ > mm/memcontrol.c | 5 +++++ > 2 files changed, 16 insertions(+) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index ce3e05e41724..fbff959c8116 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1181,6 +1181,17 @@ PAGE_SIZE multiple when read back. > high limit is used and monitored properly, this limit's > utility is limited to providing the final safety net. > > + memory.drop_cache > + A write-only single value file which exists on non-root > + cgroups. > + > + Provide a mechanism for users to actively trigger memory > + reclaim. The cgroup will be reclaimed and as many pages > + reclaimed as possible. > + > + It will broke low boundary. Because it tries to reclaim the > + memory many times, until the memory drops to a certain level. > + > memory.oom.group > A read-write single value file which exists on non-root > cgroups. The default value is "0". > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0b38b6ad547d..98646484efff 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6226,6 +6226,11 @@ static struct cftype memory_files[] = { > .write = memory_max_write, > }, > { > + .name = "drop_cache", > + .flags = CFTYPE_NOT_ON_ROOT, > + .write = mem_cgroup_force_empty_write, > + }, > + { > .name = "events", > .flags = CFTYPE_NOT_ON_ROOT, > .file_offset = offsetof(struct mem_cgroup, events_file), > -- > 2.11.0 -- Michal Hocko SUSE Labs
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