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

[Waiman Long <longman@xxxxxxxxxx>]

On 1/24/21 11:36 PM, Matthew Wilcox wrote:
> 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:
> ...
That was my original plan. After finding out there was a potentially 
conflicting patch in linux-next:

commit 7a02fa97b897 ("secretmem: add memcg accounting")

@@ -839,7 +840,7 @@ noinline int __add_to_page_cache_locked(struct page 
*page,
        page->mapping = mapping;
        page->index = offset;

-       if (!huge) {
+       if (!huge && !page_is_secretmem(page)) {
                error = mem_cgroup_charge(page, current->mm, gfp);
                if (error)
                        goto error;

Adding a boolean is an easy way out without conflicting it.

Cheers,
Longman