Re: [PATCH] mm/filemap: Adding missing mem_cgroup_uncharge() to __add_to_page_cache_locked()

[Matthew Wilcox]

On Sun, Jan 24, 2021 at 11:24:41PM -0500, Waiman Long wrote:
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 5c9d564317a5..aa0e0fb04670 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -835,6 +835,7 @@ noinline int __add_to_page_cache_locked(struct page *page,
>       XA_STATE(xas, &mapping->i_pages, offset);
>       int huge = PageHuge(page);
>       int error;
> +     bool charged = false;

I don't think we need this extra bool.

> @@ -896,6 +898,8 @@ noinline int __add_to_page_cache_locked(struct page *page,
>  
>       if (xas_error(&xas)) {
>               error = xas_error(&xas);
> +             if (charged)
> +                     mem_cgroup_uncharge(page);
>               goto error;
>       }

Better:

-               goto error;
+               goto uncharge;
...
+uncharge:
+       if (!huge)
+               mem_cgroup_uncharge(page);
 error:
...