Re: [PATCH 1/2] gfp: add __GFP_NOACCOUNT

[Michal Hocko]

On Tue 05-05-15 12:45:42, Vladimir Davydov wrote:
> Not all kmem allocations should be accounted to memcg. The following
> patch gives an example when accounting of a certain type of allocations
> to memcg can effectively result in a memory leak.

> This patch adds the __GFP_NOACCOUNT flag which if passed to kmalloc
> and friends will force the allocation to go through the root
> cgroup. It will be used by the next patch.

The name of the flag is way too generic. It is not clear that the
accounting is KMEMCG related. __GFP_NO_KMEMCG sounds better?

I was going to suggest doing per-cache rather than gfp flag and that
would actually work just fine for the kmemleak as it uses its own cache
already. But the ida_simple_get would be trickier because it doesn't use
any special cache and more over only one user seem to have a problem so
this doesn't sound like a good fit.

So I do not object to opt-out for kmemcg accounting but I really think
the name should be changed.

> Note, since in case of kmemleak enabled each kmalloc implies yet another
> allocation from the kmemleak_object cache, we add __GFP_NOACCOUNT to
> gfp_kmemleak_mask.

> Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> ---
>  include/linux/gfp.h        |    2 ++
>  include/linux/memcontrol.h |    4 ++++
>  mm/kmemleak.c              |    3 ++-
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 97a9373e61e8..37c422df2a0f 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -30,6 +30,7 @@ struct vm_area_struct;
>  #define ___GFP_HARDWALL		0x20000u
>  #define ___GFP_THISNODE		0x40000u
>  #define ___GFP_RECLAIMABLE	0x80000u
> +#define ___GFP_NOACCOUNT	0x100000u
>  #define ___GFP_NOTRACK		0x200000u
>  #define ___GFP_NO_KSWAPD	0x400000u
>  #define ___GFP_OTHER_NODE	0x800000u
> @@ -87,6 +88,7 @@ struct vm_area_struct;
>  #define __GFP_HARDWALL   ((__force gfp_t)___GFP_HARDWALL) /* Enforce hardwall cpuset memory allocs */
>  #define __GFP_THISNODE	((__force gfp_t)___GFP_THISNODE)/* No fallback, no policies */
>  #define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE) /* Page is reclaimable */
> +#define __GFP_NOACCOUNT	((__force gfp_t)___GFP_NOACCOUNT) /* Don't account to memcg */
>  #define __GFP_NOTRACK	((__force gfp_t)___GFP_NOTRACK)  /* Don't track with kmemcheck */
>  
>  #define __GFP_NO_KSWAPD	((__force gfp_t)___GFP_NO_KSWAPD)
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 72dff5fb0d0c..6c8918114804 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -463,6 +463,8 @@ memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
>  	if (!memcg_kmem_enabled())
>  		return true;
>  
> +	if (gfp & __GFP_NOACCOUNT)
> +		return true;
>  	/*
>  	 * __GFP_NOFAIL allocations will move on even if charging is not
>  	 * possible. Therefore we don't even try, and have this allocation
> @@ -522,6 +524,8 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
>  {
>  	if (!memcg_kmem_enabled())
>  		return cachep;
> +	if (gfp & __GFP_NOACCOUNT)
> +		return cachep;
>  	if (gfp & __GFP_NOFAIL)
>  		return cachep;
>  	if (in_interrupt() || (!current->mm) || (current->flags & PF_KTHREAD))
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 5405aff5a590..f0fe4f2c1fa7 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -115,7 +115,8 @@
>  #define BYTES_PER_POINTER	sizeof(void *)
>  
>  /* GFP bitmask for kmemleak internal allocations */
> -#define gfp_kmemleak_mask(gfp)	(((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \
> +#define gfp_kmemleak_mask(gfp)	(((gfp) & (GFP_KERNEL | GFP_ATOMIC | \
> +					   __GFP_NOACCOUNT)) | \
>  				 __GFP_NORETRY | __GFP_NOMEMALLOC | \
>  				 __GFP_NOWARN)
>  
> -- 
> 1.7.10.4
> 

-- 
Michal Hocko
SUSE Labs
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