Re: [PATCH 01/19] mm: fix NUMA node file count error in replace_page_cache()

[Balbir Singh]

On Fri, May 08, 2020 at 02:30:48PM -0400, Johannes Weiner wrote:
> When replacing one page with another one in the cache, we have to
> decrease the file count of the old page's NUMA node and increase the
> one of the new NUMA node, otherwise the old node leaks the count and
> the new node eventually underflows its counter.
> 
> Fixes: 74d609585d8b ("page cache: Add and replace pages using the XArray")
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
>  mm/filemap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index af1c6adad5bd..2b057b0aa882 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -808,11 +808,11 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
>  	old->mapping = NULL;
>  	/* hugetlb pages do not participate in page cache accounting. */
>  	if (!PageHuge(old))
> -		__dec_node_page_state(new, NR_FILE_PAGES);
> +		__dec_node_page_state(old, NR_FILE_PAGES);
>  	if (!PageHuge(new))
>  		__inc_node_page_state(new, NR_FILE_PAGES);
>  	if (PageSwapBacked(old))
> -		__dec_node_page_state(new, NR_SHMEM);
> +		__dec_node_page_state(old, NR_SHMEM);
>  	if (PageSwapBacked(new))
>  		__inc_node_page_state(new, NR_SHMEM);
>  	xas_unlock_irqrestore(&xas, flags);


Reviewed-by: Balbir Singh <bsingharora@xxxxxxxxx>