Messages in this thread Patch in this message | | | Date | Fri, 24 Apr 2009 11:47:17 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 09/22] Calculate the alloc_flags for allocation only once |
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On Thu, Apr 23, 2009 at 03:52:16PM -0700, Andrew Morton wrote: > On Wed, 22 Apr 2009 14:53:14 +0100 > Mel Gorman <mel@csn.ul.ie> wrote: > > > Factor out the mapping between GFP and alloc_flags only once. Once factored > > out, it only needs to be calculated once but some care must be taken. > > > > [neilb@suse.de says] > > As the test: > > > > - if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE))) > > - && !in_interrupt()) { > > - if (!(gfp_mask & __GFP_NOMEMALLOC)) { > > > > has been replaced with a slightly weaker one: > > > > + if (alloc_flags & ALLOC_NO_WATERMARKS) { > > > > Without care, this would allow recursion into the allocator via direct > > reclaim. This patch ensures we do not recurse when PF_MEMALLOC is set > > but TF_MEMDIE callers are now allowed to directly reclaim where they > > would have been prevented in the past. > > > > ... > > > > +static inline int > > +gfp_to_alloc_flags(gfp_t gfp_mask) > > +{ > > + struct task_struct *p = current; > > + int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET; > > + const gfp_t wait = gfp_mask & __GFP_WAIT; > > + > > + /* > > + * The caller may dip into page reserves a bit more if the caller > > + * cannot run direct reclaim, or if the caller has realtime scheduling > > + * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will > > + * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH). > > + */ > > + if (gfp_mask & __GFP_HIGH) > > + alloc_flags |= ALLOC_HIGH; > > + > > + if (!wait) { > > + alloc_flags |= ALLOC_HARDER; > > + /* > > + * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc. > > + * See also cpuset_zone_allowed() comment in kernel/cpuset.c. > > + */ > > + alloc_flags &= ~ALLOC_CPUSET; > > + } else if (unlikely(rt_task(p))) > > + alloc_flags |= ALLOC_HARDER; > > + > > + if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { > > + if (!in_interrupt() && > > + ((p->flags & PF_MEMALLOC) || > > + unlikely(test_thread_flag(TIF_MEMDIE)))) > > + alloc_flags |= ALLOC_NO_WATERMARKS; > > + } > > + > > + return alloc_flags; > > +} > > hm. Was there a particular reason for the explicit inline? >
Only because it was known there was only one caller.
> It's OK as it stands, but might become suboptimal if we later add a > second caller? >
This is true. As it is also in the slowpath and only called once, the following patch should make no difference to performance but potentially avoid a mistake later.
======= Uninline gfp_to_alloc_flags() in the page allocator slow path
gfp_to_alloc_flags() is in the slowpath but inlined. While there is only one caller now, a future second call would add suprising text-bloat. Uninline it now to avoid surprises later as it should have no performance impact.
Signed-off-by: Mel Gorman <mel@csn.ul.ie> --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 1c60141..f08b4cb 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1639,7 +1639,7 @@ void wake_all_kswapd(unsigned int order, struct zonelist *zonelist, wakeup_kswapd(zone, order); } -static inline int +static int gfp_to_alloc_flags(gfp_t gfp_mask) { struct task_struct *p = current;
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