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

Waiman Long
2021-01-25T14:09:37Z

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