Vaibhav Jain <vaibhav@xxxxxxxxxxxxx> wrote: > [1] Provides a way for user-space to trigger proactive reclaim by introducing > a write-only memcg file 'memory.reclaim'. However reclaim stats like number > of pages scanned and reclaimed is still not directly available to the > user-space. > > This patch proposes to extend [1] to make the memcg file 'memory.reclaim' > readable which returns the number of pages scanned / reclaimed during the > reclaim process from 'struct vmpressure' associated with each memcg. This should > let user-space asses how successful proactive reclaim triggered from memcg > 'memory.reclaim' was ? > > With the patch following command flow is expected: > > # echo "1M" > memory.reclaim > > # cat memory.reclaim > scanned 76 > reclaimed 32 I certainly appreciate the ability for shell scripts to demonstrate cgroup operations with textual interfaces, but such interface seem like they are optimized for ease of use by developers. I wonder if for runtime production use an ioctl or netlink interface has been considered for cgroup? I don't think there are any yet, but such approaches seem like a more straightforward ways to get nontrivial input/outputs from a single call (e.g. like this proposal). And they have the benefit of not requiring ascii serialization/parsing overhead. > [1]: https://lore.kernel.org/r/20220425190040.2475377-1-yosryahmed@xxxxxxxxxx > > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> > Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Signed-off-by: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx> > --- > Documentation/admin-guide/cgroup-v2.rst | 15 ++++++++++++--- > mm/memcontrol.c | 14 ++++++++++++++ > 2 files changed, 26 insertions(+), 3 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 27ebef2485a3..44610165261d 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1209,18 +1209,27 @@ PAGE_SIZE multiple when read back. > utility is limited to providing the final safety net. > > memory.reclaim > - A write-only nested-keyed file which exists for all cgroups. > + A nested-keyed file which exists for all cgroups. > > - This is a simple interface to trigger memory reclaim in the > - target cgroup. > + This is a simple interface to trigger memory reclaim and retrieve > + reclaim stats in the target cgroup. > > This file accepts a single key, the number of bytes to reclaim. > No nested keys are currently supported. > > + Reading the file returns number of pages scanned and number of > + pages reclaimed from the memcg. This information fetched from > + vmpressure info associated with each cgroup. > + > Example:: > > echo "1G" > memory.reclaim > > + cat memory.reclaim > + > + scanned 78 > + reclaimed 30 > + > The interface can be later extended with nested keys to > configure the reclaim behavior. For example, specify the > type of memory to reclaim from (anon, file, ..). > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 2e2bfbed4717..9e43580a8726 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6423,6 +6423,19 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of, > return nbytes; > } > > +static int memory_reclaim_show(struct seq_file *m, void *v) > +{ > + struct mem_cgroup *memcg = mem_cgroup_from_seq(m); > + struct vmpressure *vmpr = memcg_to_vmpressure(memcg); > + > + spin_lock(&vmpr->sr_lock); > + seq_printf(m, "scanned %lu\nreclaimed %lu\n", > + vmpr->scanned, vmpr->reclaimed); > + spin_unlock(&vmpr->sr_lock); > + > + return 0; > +} > + > static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, > size_t nbytes, loff_t off) > { > @@ -6525,6 +6538,7 @@ static struct cftype memory_files[] = { > .name = "reclaim", > .flags = CFTYPE_NS_DELEGATABLE, > .write = memory_reclaim, > + .seq_show = memory_reclaim_show, > }, > { } /* terminate */ > };
