[PATCH v2] mm/slub: don't wait for high-order page allocation

[PATCH v2] mm/slub: don't wait for high-order page allocation

[Joonsoo Kim]

Almost description is copied from commit fb05e7a89f50
("net: don't wait for order-3 page allocation").

I saw excessive direct memory reclaim/compaction triggered by slub.
This causes performance issues and add latency. Slub uses high-order
allocation to reduce internal fragmentation and management overhead. But,
direct memory reclaim/compaction has high overhead and the benefit of
high-order allocation can't compensate the overhead of both work.

This patch makes auxiliary high-order allocation atomic. If there is
no memory pressure and memory isn't fragmented, the alloction will still
success, so we don't sacrifice high-order allocation's benefit here.
If the atomic allocation fails, direct memory reclaim/compaction will not
be triggered, allocation fallback to low-order immediately, hence
the direct memory reclaim/compaction overhead is avoided. In the
allocation failure case, kswapd is waken up and trying to make high-order
freepages, so allocation could success next time.

Following is the test to measure effect of this patch.

System: QEMU, CPU 8, 512 MB
Mem: 25% memory is allocated at random position to make fragmentation.
 Memory-hogger occupies 150 MB memory.
Workload: hackbench -g 20 -l 1000

Average result by 10 runs (Base va Patched)

elapsed_time(s): 4.3468 vs 2.9838
compact_stall: 461.7 vs 73.6
pgmigrate_success: 28315.9 vs 7256.1

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 mm/slub.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 257283f..52b9025 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1364,6 +1364,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 	 * so we fall-back to the minimum order allocation.
 	 */
 	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
+	if ((alloc_gfp & __GFP_WAIT) && oo_order(oo) > oo_order(s->min))
+		alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~__GFP_WAIT;
 
 	page = alloc_slab_page(s, alloc_gfp, node, oo);
 	if (unlikely(!page)) {
-- 
1.9.1

Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

[Michal Hocko]

On Fri 07-08-15 11:10:03, Joonsoo Kim wrote:
[...]
> diff --git a/mm/slub.c b/mm/slub.c
> index 257283f..52b9025 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1364,6 +1364,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
>  	 * so we fall-back to the minimum order allocation.
>  	 */
>  	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
> +	if ((alloc_gfp & __GFP_WAIT) && oo_order(oo) > oo_order(s->min))
> +		alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~__GFP_WAIT;

Wouldn't it be preferable to "fix" the __GFP_WAIT behavior than spilling
__GFP_NOMEMALLOC around the kernel? GFP flags are getting harder and
harder to use right and that is a signal we should thing about it and
unclutter the current state.

>  
>  	page = alloc_slab_page(s, alloc_gfp, node, oo);
>  	if (unlikely(!page)) {
> -- 
> 1.9.1

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

[Joonsoo Kim]

On Fri, Aug 07, 2015 at 05:05:01PM +0200, Michal Hocko wrote:
> On Fri 07-08-15 11:10:03, Joonsoo Kim wrote:
> [...]
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 257283f..52b9025 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1364,6 +1364,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> >  	 * so we fall-back to the minimum order allocation.
> >  	 */
> >  	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
> > +	if ((alloc_gfp & __GFP_WAIT) && oo_order(oo) > oo_order(s->min))
> > +		alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~__GFP_WAIT;
> 
> Wouldn't it be preferable to "fix" the __GFP_WAIT behavior than spilling
> __GFP_NOMEMALLOC around the kernel? GFP flags are getting harder and
> harder to use right and that is a signal we should thing about it and
> unclutter the current state.

Maybe, it is preferable. Could you try that?

Anyway, it is separate issue so I don't want pending this patch until
that change.

Thanks.

Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

[Michal Hocko]

On Mon 10-08-15 09:40:22, Joonsoo Kim wrote:
> On Fri, Aug 07, 2015 at 05:05:01PM +0200, Michal Hocko wrote:
> > On Fri 07-08-15 11:10:03, Joonsoo Kim wrote:
> > [...]
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index 257283f..52b9025 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -1364,6 +1364,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> > >  	 * so we fall-back to the minimum order allocation.
> > >  	 */
> > >  	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
> > > +	if ((alloc_gfp & __GFP_WAIT) && oo_order(oo) > oo_order(s->min))
> > > +		alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~__GFP_WAIT;
> > 
> > Wouldn't it be preferable to "fix" the __GFP_WAIT behavior than spilling
> > __GFP_NOMEMALLOC around the kernel? GFP flags are getting harder and
> > harder to use right and that is a signal we should thing about it and
> > unclutter the current state.
> 
> Maybe, it is preferable. Could you try that?

I will try to cook up something during the week.

> Anyway, it is separate issue so I don't want pending this patch until
> that change.

OK, fair enough, at least this one is in mm proper...
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

[David Rientjes]

On Fri, 7 Aug 2015, Joonsoo Kim wrote:

> Almost description is copied from commit fb05e7a89f50
> ("net: don't wait for order-3 page allocation").
> 
> I saw excessive direct memory reclaim/compaction triggered by slub.
> This causes performance issues and add latency. Slub uses high-order
> allocation to reduce internal fragmentation and management overhead. But,
> direct memory reclaim/compaction has high overhead and the benefit of
> high-order allocation can't compensate the overhead of both work.
> 
> This patch makes auxiliary high-order allocation atomic. If there is
> no memory pressure and memory isn't fragmented, the alloction will still
> success, so we don't sacrifice high-order allocation's benefit here.
> If the atomic allocation fails, direct memory reclaim/compaction will not
> be triggered, allocation fallback to low-order immediately, hence
> the direct memory reclaim/compaction overhead is avoided. In the
> allocation failure case, kswapd is waken up and trying to make high-order
> freepages, so allocation could success next time.
> 
> Following is the test to measure effect of this patch.
> 
> System: QEMU, CPU 8, 512 MB
> Mem: 25% memory is allocated at random position to make fragmentation.
>  Memory-hogger occupies 150 MB memory.
> Workload: hackbench -g 20 -l 1000
> 
> Average result by 10 runs (Base va Patched)
> 
> elapsed_time(s): 4.3468 vs 2.9838
> compact_stall: 461.7 vs 73.6
> pgmigrate_success: 28315.9 vs 7256.1
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Acked-by: David Rientjes <rientjes@google.com>