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Date:   Mon, 4 Nov 2019 14:58:05 -0500
From:   Brian Foster <bfoster@redhat.com>
To:     Dave Chinner <david@fromorbit.com>
Cc:     linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 14/28] mm: reclaim_state records pages reclaimed, not
 slabs
Message-ID: <20191104195805.GE10665@bfoster>
References: <20191031234618.15403-1-david@fromorbit.com>
 <20191031234618.15403-15-david@fromorbit.com>
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On Fri, Nov 01, 2019 at 10:46:04AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>=20
> 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.
>=20
> No logic changes, just replacing open coded checks with a simple
> wrapper.
>=20
> 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(-)
>=20
> 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,
>  =09=09=09=09__count_vm_events(KSWAPD_INODESTEAL, reap);
>  =09=09=09else
>  =09=09=09=09__count_vm_events(PGINODESTEAL, reap);
> -=09=09=09if (current->reclaim_state)
> -=09=09=09=09current->reclaim_state->reclaimed_slab +=3D reap;
> +=09=09=09current_reclaim_account_pages(reap);
>  =09=09}
>  =09=09iput(inode);
>  =09=09spin_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(
> =20
>  =09=09=09__free_page(page);
>  =09=09}
> -=09=09if (current->reclaim_state)
> -=09=09=09current->reclaim_state->reclaimed_slab +=3D
> -=09=09=09=09=09=09=09bp->b_page_count;
> +=09=09current_reclaim_account_pages(bp->b_page_count);
>  =09} else if (bp->b_flags & _XBF_KMEM)
>  =09=09kmem_free(bp->b_addr);
>  =09_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 {
> =20
>  /*
>   * 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 {
> -=09unsigned long reclaimed_slab;
> +=09unsigned long=09reclaimed_pages;=09/* pages freed by shrinkers */
>  };
> =20
> +/*
> + * 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 t=
hem.
> + * 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 w=
ell 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)
> +{
> +=09if (current->reclaim_state)
> +=09=09current->reclaim_state->reclaimed_pages +=3D nr_pages;
> +}
> +
>  #ifdef __KERNEL__
> =20
>  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 *cache=
p, struct page *page)
>  =09page_mapcount_reset(page);
>  =09page->mapping =3D NULL;
> =20
> -=09if (current->reclaim_state)
> -=09=09current->reclaim_state->reclaimed_slab +=3D 1 << order;
> +=09current_reclaim_account_pages(1 << order);
>  =09uncharge_slab_page(page, order, cachep);
>  =09__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)
>  {
>  =09struct page *sp =3D virt_to_page(b);
> =20
> -=09if (current->reclaim_state)
> -=09=09current->reclaim_state->reclaimed_slab +=3D 1 << order;
> -
> +=09current_reclaim_account_pages(1 << order);
>  =09mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE,
>  =09=09=09    -(1 << order));
>  =09__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, struc=
t page *page)
>  =09__ClearPageSlab(page);
> =20
>  =09page->mapping =3D NULL;
> -=09if (current->reclaim_state)
> -=09=09current->reclaim_state->reclaimed_slab +=3D pages;
> +=09current_reclaim_account_pages(pages);
>  =09uncharge_slab_page(page, order, s);
>  =09__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 sc=
an_control *sc)
>  =09=09} while ((memcg =3D mem_cgroup_iter(root, memcg, NULL)));
> =20
>  =09=09if (reclaim_state) {
> -=09=09=09sc->nr_reclaimed +=3D reclaim_state->reclaimed_slab;
> -=09=09=09reclaim_state->reclaimed_slab =3D 0;
> +=09=09=09sc->nr_reclaimed +=3D reclaim_state->reclaimed_pages;
> +=09=09=09reclaim_state->reclaimed_pages =3D 0;
>  =09=09}
> =20
>  =09=09/* Record the subtree's reclaim efficiency */
> --=20
> 2.24.0.rc0
>=20