Re: [Resend PATCH 2/6] mm/memcg: remove useless check on page->mem_cgroup

Michal Hocko
2020-08-13T06:20:49Z

On Wed 12-08-20 11:25:53, Alex Shi wrote:
> >From 999b0fe5fc65865c3b59ff28500d45572a4a9570 Mon Sep 17 00:00:00 2001
> From: Alex Shi <alex.shi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
> Date: Wed, 5 Aug 2020 21:02:30 +0800
> Subject: [PATCH 2/6] mm/memcg: bail out early from swap accounting when memcg
> is disabled
>
> If we disabled memcg by cgroup_disable=memory, page->memcg will be NULL
> and so the charge is skipped and that will trigger a warning like below.
> Let's return from the funcs earlier.
>
> ---[ end trace f1f34bfc3b32ed2f ]---
> anon flags:0x5005b48008000d(locked|uptodate|dirty|swapbacked)
> raw: 005005b48008000d dead000000000100 dead000000000122 ffff8897c7c76ad1
> raw: 0000000000000022 0000000000000000 0000000200000000 0000000000000000
> page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg)

Yes this is better. It would be even more informative if you added the
backtrace.

> Signed-off-by: Alex Shi <alex.shi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
> Reviewed-by: Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>
> Acked-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
> Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Cc: Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org
> Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> ---
> mm/memcontrol.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 299382fc55a9..419cf565f40b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7098,6 +7098,9 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
> VM_BUG_ON_PAGE(PageLRU(page), page);
> VM_BUG_ON_PAGE(page_count(page), page);
>
> + if (mem_cgroup_disabled())
> + return;
> +
> if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
> return;
>
> @@ -7163,6 +7166,9 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
> struct mem_cgroup *memcg;
> unsigned short oldid;
>
> + if (mem_cgroup_disabled())
> + return 0;
> +
> if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> return 0;
>
> --
> 1.8.3.1

--
Michal Hocko
SUSE Labs