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

Brian Foster
2019-11-04T19:58:13Z

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
>