linux-kernel - Re: [PATCH 09/12] mm, slub: split out allocations from pre/post hooks

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Date:   Mon, 28 Nov 2022 22:06:15 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, patches@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/12] mm, slub: split out allocations from pre/post hooks

On Mon, Nov 28, 2022 at 12:01:39AM +0100, Vlastimil Babka wrote:
> On 11/27/22 11:54, Hyeonggon Yoo wrote:
> > On Mon, Nov 21, 2022 at 06:11:59PM +0100, Vlastimil Babka wrote:
> >> In the following patch we want to introduce CONFIG_SLUB_TINY allocation
> >> paths that don't use the percpu slab. To prepare, refactor the
> >> allocation functions:
> >> 
> >> Split out __slab_alloc_node() from slab_alloc_node() where the former
> >> does the actual allocation and the latter calls the pre/post hooks.
> >> 
> >> Analogically, split out __kmem_cache_alloc_bulk() from
> >> kmem_cache_alloc_bulk().
> >> 
> >> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> >> ---
> >>  mm/slub.c | 127 +++++++++++++++++++++++++++++++++---------------------
> >>  1 file changed, 77 insertions(+), 50 deletions(-)
> > 
> > [...]
> > 
> >> +
> >> +/* Note that interrupts must be enabled when calling this function. */
> >> +int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
> >> +			  void **p)
> >> +{
> >> +	int i;
> >> +	struct obj_cgroup *objcg = NULL;
> >> +
> >> +	/* memcg and kmem_cache debug support */
> >> +	s = slab_pre_alloc_hook(s, NULL, &objcg, size, flags);
> >> +	if (unlikely(!s))
> >> +		return false;
> >> +
> >> +	i = __kmem_cache_alloc_bulk(s, flags, size, p, objcg);
> >> +
> >> +	/*
> >> +	 * memcg and kmem_cache debug support and memory initialization.
> >> +	 * Done outside of the IRQ disabled fastpath loop.
> >> +	 */
> >> +	if (i != 0)
> >> +		slab_post_alloc_hook(s, objcg, flags, size, p,
> >> +				slab_want_init_on_alloc(flags, s));
> > 
> > This patch looks mostly good but wondering what happens if someone calls it with size == 0
> > so it does not call slab_post_alloc_hook()?
> 
> Hmm looks like in that case we miss doing obj_cgroup_put(objcg) in
> memcg_slab_post_alloc_hook(). Good catch, thanks!
> 
> Fixing up, also a "return false" from int function
> (existed also before this patch).
> 
> ----8<----
> diff --git a/mm/slub.c b/mm/slub.c
> index b74c4664160e..88f0ce49caab 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3888,10 +3888,13 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
>  	int i;
>  	struct obj_cgroup *objcg = NULL;
>  
> +	if (!size)
> +		return 0;
> +
>  	/* memcg and kmem_cache debug support */
>  	s = slab_pre_alloc_hook(s, NULL, &objcg, size, flags);
>  	if (unlikely(!s))
> -		return false;
> +		return 0;
>  
>  	i = __kmem_cache_alloc_bulk(s, flags, size, p, objcg);

With that,

Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

Thanks!

-- 
Thanks,
Hyeonggon