Re: [PATCH v1] proc: Implement /proc/self/meminfo

From: Chris Down
Date: Thu Jun 03 2021 - 07:35:17 EST

Hi Alexey,

legion@xxxxxxxxxx writes:
From: Alexey Gladkov <legion@xxxxxxxxxx>
The /proc/meminfo contains information regardless of the cgroups
restrictions. This file is still widely used [1]. This means that all
these programs will not work correctly inside container [2][3][4]. Some
programs try to respect the cgroups limits, but not all of them
implement support for all cgroup versions [5].

Correct information can be obtained from cgroups, but this requires the
cgroups to be available inside container and the correct version of
cgroups to be supported.

Then they should add support for it. We already export these metrics as part of cgroups and plenty of applications like Docker, podman, containerd, systemd, runc, etc already support it.

Putting stuff in /proc to get around the problem of "some other metric I need might not be exported to a container" is not a very compelling argument. If they want it, then export it to the container...

Ultimately, if they're going to have to add support for a new /proc/self/meminfo file anyway, these use cases should just do it properly through the already supported APIs.

+ for_each_online_node(nid)
+ mem_cgroup_nr_pages(memcg, nid, mi->pages);
+ mi->slab_reclaimable = memcg_page_state(memcg, NR_SLAB_RECLAIMABLE_B);
+ mi->slab_unreclaimable = memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE_B);
+ mi->cached = memcg_page_state(memcg, NR_FILE_PAGES);
+ mi->swapcached = memcg_page_state(memcg, NR_SWAPCACHE);
+ mi->anon_pages = memcg_page_state(memcg, NR_ANON_MAPPED);
+ mi->mapped = memcg_page_state(memcg, NR_FILE_MAPPED);
+ mi->nr_pagetable = memcg_page_state(memcg, NR_PAGETABLE);
+ mi->dirty_pages = memcg_page_state(memcg, NR_FILE_DIRTY);
+ mi->writeback_pages = memcg_page_state(memcg, NR_WRITEBACK);

This presents an extraordinarily confusing API. A cgroup can contain more than one process, so it's not right to present this information as "meminfo" in /proc/self when these statistics may not have any relation to the current task under question.