linux-kernel - Re: [PATCH v2 3/6] memcg: only account kmem allocations marked as __GFP

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Date:	Thu, 12 Nov 2015 17:04:10 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Greg Thelen <gthelen@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/6] memcg: only account kmem allocations marked as
 __GFP_ACCOUNT

On Tue 10-11-15 21:34:04, Vladimir Davydov wrote:
> Black-list kmem accounting policy (aka __GFP_NOACCOUNT) turned out to be
> fragile and difficult to maintain, because there seem to be many more
> allocations that should not be accounted than those that should be.
> Besides, false accounting an allocation might result in much worse
> consequences than not accounting at all, namely increased memory
> consumption due to pinned dead kmem caches.
> 
> So this patch switches kmem accounting to the white-policy: now only
> those kmem allocations that are marked as __GFP_ACCOUNT are accounted to
> memcg. Currently, no kmem allocations are marked like this. The
> following patches will mark several kmem allocations that are known to
> be easily triggered from userspace and therefore should be accounted to
> memcg.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>

As mentioned previously I would simply squash 1-3 into a single patch.
Anyway
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  include/linux/gfp.h        | 4 ++++
>  include/linux/memcontrol.h | 2 ++
>  mm/page_alloc.c            | 3 ++-
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 2b917ce34efc..61305a492356 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_ACCOUNT		0x100000u
>  #define ___GFP_NOTRACK		0x200000u
>  #define ___GFP_NO_KSWAPD	0x400000u
>  #define ___GFP_OTHER_NODE	0x800000u
> @@ -90,6 +91,8 @@ 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_ACCOUNT	((__force gfp_t)___GFP_ACCOUNT)	/* Account to memcg (only relevant
> +							 * to kmem allocations) */
>  #define __GFP_NOTRACK	((__force gfp_t)___GFP_NOTRACK)  /* Don't track with kmemcheck */
>  
>  #define __GFP_NO_KSWAPD	((__force gfp_t)___GFP_NO_KSWAPD)
> @@ -112,6 +115,7 @@ struct vm_area_struct;
>  #define GFP_NOIO	(__GFP_WAIT)
>  #define GFP_NOFS	(__GFP_WAIT | __GFP_IO)
>  #define GFP_KERNEL	(__GFP_WAIT | __GFP_IO | __GFP_FS)
> +#define GFP_KERNEL_ACCOUNT	(GFP_KERNEL | __GFP_ACCOUNT)
>  #define GFP_TEMPORARY	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
>  			 __GFP_RECLAIMABLE)
>  #define GFP_USER	(__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL)
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 2103f36b3bd3..c9d9a8e7b45f 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -773,6 +773,8 @@ static inline bool __memcg_kmem_bypass(gfp_t gfp)
>  {
>  	if (!memcg_kmem_enabled())
>  		return true;
> +	if (!(gfp & __GFP_ACCOUNT))
> +		return true;
>  	if (in_interrupt() || (!current->mm) || (current->flags & PF_KTHREAD))
>  		return true;
>  	return false;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 446bb36ee59d..8e22f5b27de0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3420,7 +3420,8 @@ EXPORT_SYMBOL(__free_page_frag);
>  
>  /*
>   * alloc_kmem_pages charges newly allocated pages to the kmem resource counter
> - * of the current memory cgroup.
> + * of the current memory cgroup if __GFP_ACCOUNT is set, other than that it is
> + * equivalent to alloc_pages.
>   *
>   * It should be used when the caller would like to use kmalloc, but since the
>   * allocation is large, it has to fall back to the page allocator.
> -- 
> 2.1.4

-- 
Michal Hocko
SUSE Labs
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