Re: [PATCH 14/28] mm: reclaim_state records pages reclaimed, not slabs

[Brian Foster <bfoster@redhat.com>]

On Fri, Nov 01, 2019 at 10:46:04AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Add a wrapper to account for page freeing in shrinker reclaim so
> that the high level scanning accounts for all the memory freed
> during a shrinker scan.
> 
> No logic changes, just replacing open coded checks with a simple
> wrapper.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

Looks straightforward:

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/inode.c           |  3 +--
>  fs/xfs/xfs_buf.c     |  4 +---
>  include/linux/swap.h | 20 ++++++++++++++++++--
>  mm/slab.c            |  3 +--
>  mm/slob.c            |  4 +---
>  mm/slub.c            |  3 +--
>  mm/vmscan.c          |  4 ++--
>  7 files changed, 25 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index fef457a42882..a77caf216659 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -764,8 +764,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
>  				__count_vm_events(KSWAPD_INODESTEAL, reap);
>  			else
>  				__count_vm_events(PGINODESTEAL, reap);
> -			if (current->reclaim_state)
> -				current->reclaim_state->reclaimed_slab += reap;
> +			current_reclaim_account_pages(reap);
>  		}
>  		iput(inode);
>  		spin_lock(lru_lock);
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index d34e5d2edacd..55b082bc53b3 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -324,9 +324,7 @@ xfs_buf_free(
>  
>  			__free_page(page);
>  		}
> -		if (current->reclaim_state)
> -			current->reclaim_state->reclaimed_slab +=
> -							bp->b_page_count;
> +		current_reclaim_account_pages(bp->b_page_count);
>  	} else if (bp->b_flags & _XBF_KMEM)
>  		kmem_free(bp->b_addr);
>  	_xfs_buf_free_pages(bp);
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 063c0c1e112b..72b855fe20b0 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -126,12 +126,28 @@ union swap_header {
>  
>  /*
>   * current->reclaim_state points to one of these when a task is running
> - * memory reclaim
> + * memory reclaim. It is typically used by shrinkers to return reclaim
> + * information back to the main vmscan loop.
>   */
>  struct reclaim_state {
> -	unsigned long reclaimed_slab;
> +	unsigned long	reclaimed_pages;	/* pages freed by shrinkers */
>  };
>  
> +/*
> + * When code frees a page that may be run from a memory reclaim context, it
> + * needs to account for the pages it frees so memory reclaim can track them.
> + * Slab memory that is freed is accounted via this mechanism, so this is not
> + * necessary for slab or heap memory being freed. However, if the object being
> + * freed frees pages directly, then those pages should be accounted as well when
> + * in memory reclaim. This helper function takes care accounting for the pages
> + * being reclaimed when it is required.
> + */
> +static inline void current_reclaim_account_pages(int nr_pages)
> +{
> +	if (current->reclaim_state)
> +		current->reclaim_state->reclaimed_pages += nr_pages;
> +}
> +
>  #ifdef __KERNEL__
>  
>  struct address_space;
> diff --git a/mm/slab.c b/mm/slab.c
> index 66e5d8032bae..419be005f41a 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1395,8 +1395,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct page *page)
>  	page_mapcount_reset(page);
>  	page->mapping = NULL;
>  
> -	if (current->reclaim_state)
> -		current->reclaim_state->reclaimed_slab += 1 << order;
> +	current_reclaim_account_pages(1 << order);
>  	uncharge_slab_page(page, order, cachep);
>  	__free_pages(page, order);
>  }
> diff --git a/mm/slob.c b/mm/slob.c
> index fa53e9f73893..c54a7eeee86d 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order)
>  {
>  	struct page *sp = virt_to_page(b);
>  
> -	if (current->reclaim_state)
> -		current->reclaim_state->reclaimed_slab += 1 << order;
> -
> +	current_reclaim_account_pages(1 << order);
>  	mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE,
>  			    -(1 << order));
>  	__free_pages(sp, order);
> diff --git a/mm/slub.c b/mm/slub.c
> index b25c807a111f..478554082079 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1746,8 +1746,7 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
>  	__ClearPageSlab(page);
>  
>  	page->mapping = NULL;
> -	if (current->reclaim_state)
> -		current->reclaim_state->reclaimed_slab += pages;
> +	current_reclaim_account_pages(pages);
>  	uncharge_slab_page(page, order, s);
>  	__free_pages(page, order);
>  }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7a8256322150..967e3d3c7748 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2870,8 +2870,8 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>  		} while ((memcg = mem_cgroup_iter(root, memcg, NULL)));
>  
>  		if (reclaim_state) {
> -			sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> -			reclaim_state->reclaimed_slab = 0;
> +			sc->nr_reclaimed += reclaim_state->reclaimed_pages;
> +			reclaim_state->reclaimed_pages = 0;
>  		}
>  
>  		/* Record the subtree's reclaim efficiency */
> -- 
> 2.24.0.rc0
>