Re: [PATCH 1/4] slab: do ClearSlabPfmemalloc() for all pages of slab

[JoonSoo Kim]

2012/9/7 Mel Gorman <mgorman@xxxxxxx>:
> This churns code a lot more than is necessary. How about this as a
> replacement patch?
>
> ---8<---
> From: Joonsoo Kim <js1304@xxxxxxxxx>
> Subject: [PATCH] slab: do ClearSlabPfmemalloc() for all pages of slab
>
> Right now, we call ClearSlabPfmemalloc() for first page of slab when we
> clear SlabPfmemalloc flag. This is fine for most swap-over-network use
> cases as it is expected that order-0 pages are in use. Unfortunately it
> is possible that that __ac_put_obj() checks SlabPfmemalloc on a tail page
> and while this is harmless, it is sloppy. This patch ensures that the head
> page is always used.
>
> [mgorman@xxxxxxx: Easier implementation, changelog cleanup]
> Signed-off-by: Joonsoo Kim <js1304@xxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
>  mm/slab.c |   12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 811af03..590d52a 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1032,7 +1032,7 @@ static void *__ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
>  {
>         if (unlikely(pfmemalloc_active)) {
>                 /* Some pfmemalloc slabs exist, check if this is one */
> -               struct page *page = virt_to_page(objp);
> +               struct page *page = virt_to_head_page(objp);
>                 if (PageSlabPfmemalloc(page))
>                         set_obj_pfmemalloc(&objp);
>         }
> @@ -1919,12 +1919,10 @@ static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
>         else
>                 add_zone_page_state(page_zone(page),
>                         NR_SLAB_UNRECLAIMABLE, nr_pages);
> -       for (i = 0; i < nr_pages; i++) {
> +       for (i = 0; i < nr_pages; i++)
>                 __SetPageSlab(page + i);
> -
> -               if (page->pfmemalloc)
> -                       SetPageSlabPfmemalloc(page + i);
> -       }
> +       if (page->pfmemalloc)
> +               SetPageSlabPfmemalloc(page);
>
>         if (kmemcheck_enabled && !(cachep->flags & SLAB_NOTRACK)) {
>                 kmemcheck_alloc_shadow(page, cachep->gfporder, flags, nodeid);
> @@ -1955,9 +1953,9 @@ static void kmem_freepages(struct kmem_cache *cachep, void *addr)
>         else
>                 sub_zone_page_state(page_zone(page),
>                                 NR_SLAB_UNRECLAIMABLE, nr_freed);
> +       __ClearPageSlabPfmemalloc(page);
>         while (i--) {
>                 BUG_ON(!PageSlab(page));
> -               __ClearPageSlabPfmemalloc(page);
>                 __ClearPageSlab(page);
>                 page++;
>         }

Okay.
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