Re: [PATCH 4/5] khugepaged: remove unnecessary mem_cgroup_uncharge() in collapse_[file|huge_page]

[Kirill A. Shutemov]

On Thu, Mar 04, 2021 at 07:30:12AM -0500, Miaohe Lin wrote:
> Since commit 7ae88534cdd9 ("mm: move mem_cgroup_uncharge out of
> __page_cache_release()"), the mem_cgroup will be uncharged when hpage is
> freed. Uncharge mem_cgroup here is harmless but it looks confusing and
> buggy: if mem_cgroup charge failed, we will call mem_cgroup_uncharge()
> uncorrectly in error path because hpage is not IS_ERR_OR_NULL().
> 
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>

Hm. I'm not sure about this patch.

For !NUMA the page will get allocated and freed very early: in
khugepaged_do_scan() and with the change mem_cgroup_charge() may get
called twice for two different mm_structs.

Is it safe?

-- 
 Kirill A. Shutemov