Re: [PATCH -mm 1/2] mm: vmscan: account slab pages on memcg reclaim

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Jan 12, 2015 at 12:30:37PM +0300, Vladimir Davydov wrote:
> Since try_to_free_mem_cgroup_pages() can now call slab shrinkers, we
> should initialize reclaim_state and account reclaimed slab pages in
> scan_control->nr_reclaimed.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
> ---
>  mm/vmscan.c |   33 ++++++++++++++++++++++-----------
>  1 file changed, 22 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 16f3e45742d6..b2c041139a51 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -367,13 +367,16 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>   * the ->seeks setting of the shrink function, which indicates the
>   * cost to recreate an object relative to that of an LRU page.
>   *
> - * Returns the number of reclaimed slab objects.
> + * Returns the number of reclaimed slab objects. The number of reclaimed
> + * pages is added to *@ret_nr_reclaimed.
>
>  static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
>  				 struct mem_cgroup *memcg,
>  				 unsigned long nr_scanned,
> -				 unsigned long nr_eligible)
> +				 unsigned long nr_eligible,
> +				 unsigned long *ret_nr_reclaimed)

Can't we just return the number of pages directly from this function?

> @@ -426,7 +434,7 @@ void drop_slab_node(int nid)
>  		freed = 0;
>  		do {
>  			freed += shrink_slab(GFP_KERNEL, nid, memcg,
> -					     1000, 1000);
> +					     1000, 1000, &nr_reclaimed);
>  		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
>  	} while (freed > 10);

This is the only caller that cares about the return value, and it's a
magic number that could probably be changed to comparing with a magic
number of pages instead.

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