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

Mel Gorman
2011-05-11T21:10:53Z

On Wed, May 11, 2011 at 01:38:44PM -0700, David Rientjes wrote:
> 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.
>

True. I'll remove it in a V2 but I won't respin just yet.

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

--
Mel Gorman
SUSE Labs