Re: [PATCH 1/2] mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled

[Shakeel Butt]

On Thu, Mar 18, 2021 at 10:49 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> Since commit 2d1c498072de ("mm: memcontrol: make swap tracking an
> integral part of memory control"), the cgroup swap arrays are used to
> track memory ownership at the time of swap readahead and swapoff, even
> if swap space *accounting* has been turned off by the user via
> swapaccount=0 (which sets cgroup_memory_noswap).
>
> However, the patch was overzealous: by simply dropping the
> cgroup_memory_noswap conditionals in the swapon, swapoff and uncharge
> path, it caused the cgroup arrays being allocated even when the memory
> controller as a whole is disabled. This is a waste of that memory.
>
> Restore mem_cgroup_disabled() checks, implied previously by
> cgroup_memory_noswap, in the swapon, swapoff, and swap_entry_free
> callbacks.
>
> Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control")
> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>