Re: [PATCH 2/3] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations

David Rientjes
2011-05-11T20:39:14Z

On Wed, 11 May 2011, Mel Gorman wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9f8a97b..057f1e2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1972,6 +1972,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> {
> int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
> const gfp_t wait = gfp_mask & __GFP_WAIT;
> + const gfp_t can_wake_kswapd = !(gfp_mask & __GFP_NO_KSWAPD);
>
> /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
> BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
> @@ -1984,7 +1985,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> */
> alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH);
>
> - if (!wait) {
> + if (!wait && can_wake_kswapd) {
> /*
> * Not worth trying to allocate harder for
> * __GFP_NOMEMALLOC even if it can't schedule.
> diff --git a/mm/slub.c b/mm/slub.c
> index 98c358d..1071723 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1170,7 +1170,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> * Let the initial higher-order allocation fail under memory pressure
> * so we fall-back to the minimum order allocation.
> */
> - alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL;
> + alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) &
> + ~(__GFP_NOFAIL | __GFP_WAIT);

__GFP_NORETRY is a no-op without __GFP_WAIT.

>
> page = alloc_slab_page(alloc_gfp, node, oo);
> if (unlikely(!page)) {