Date: Tue, 9 Jun 2015 09:26:39 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: linux-kernel@vger.kernel.org
Cc: cl@linux.com, brouer@redhat.com, penberg@kernel.org, rientjes@google.com,
        mm-commits@vger.kernel.org
Subject: Re: + slub-bulk-alloc-extract-objects-from-the-per-cpu-slab.patch
 added to -mm tree
Message-ID: <20150609002639.GB9687@js1304-P5Q-DELUXE>
References: <5525b159.BpuUD6FQt89EaGh/%akpm@linux-foundation.org>
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On Wed, Apr 08, 2015 at 03:53:13PM -0700, akpm@linux-foundation.org wrote:
> 
> The patch titled
>      Subject: slub bulk alloc: extract objects from the per cpu slab
> has been added to the -mm tree.  Its filename is
>      slub-bulk-alloc-extract-objects-from-the-per-cpu-slab.patch
> 
> This patch should soon appear at
>     http://ozlabs.org/~akpm/mmots/broken-out/slub-bulk-alloc-extract-objects-from-the-per-cpu-slab.patch
> and later at
>     http://ozlabs.org/~akpm/mmotm/broken-out/slub-bulk-alloc-extract-objects-from-the-per-cpu-slab.patch
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
> 
> ------------------------------------------------------
> From: Christoph Lameter <cl@linux.com>
> Subject: slub bulk alloc: extract objects from the per cpu slab
> 
> First piece: acceleration of retrieval of per cpu objects
> 
> If we are allocating lots of objects then it is advantageous to disable
> interrupts and avoid the this_cpu_cmpxchg() operation to get these objects
> faster.  Note that we cannot do the fast operation if debugging is
> enabled.  Note also that the requirement of having interrupts disabled
> avoids having to do processor flag operations.
> 
> Allocate as many objects as possible in the fast way and then fall back to
> the generic implementation for the rest of the objects.
> 
> Signed-off-by: Christoph Lameter <cl@linux.com>
> Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  mm/slub.c |   27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff -puN mm/slub.c~slub-bulk-alloc-extract-objects-from-the-per-cpu-slab mm/slub.c
> --- a/mm/slub.c~slub-bulk-alloc-extract-objects-from-the-per-cpu-slab
> +++ a/mm/slub.c
> @@ -2759,7 +2759,32 @@ EXPORT_SYMBOL(kmem_cache_free_bulk);
>  bool kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
>  								void **p)
>  {
> -	return kmem_cache_alloc_bulk(s, flags, size, p);
> +	if (!kmem_cache_debug(s)) {
> +		struct kmem_cache_cpu *c;
> +
> +		/* Drain objects in the per cpu slab */
> +		local_irq_disable();
> +		c = this_cpu_ptr(s->cpu_slab);
> +
> +		while (size) {
> +			void *object = c->freelist;
> +
> +			if (!object)
> +				break;
> +
> +			c->freelist = get_freepointer(s, object);
> +			*p++ = object;
> +			size--;
> +
> +			if (unlikely(flags & __GFP_ZERO))
> +				memset(object, 0, s->object_size);
> +		}
> +		c->tid = next_tid(c->tid);
> +
> +		local_irq_enable();
> +	}
> +
> +	return __kmem_cache_alloc_bulk(s, flags, size, p);

Hello,

So, if __kmem_cache_alloc_bulk() fails, all allocated objects in array
should be freed, but, __kmem_cache_alloc_bulk() can't know
about objects allocated by this slub specific kmem_cache_alloc_bulk()
function. Please fix it.

Thanks.
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