Received-SPF: pass (google.com: domain of linux-kernel+bounces-143982-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Sat, 13 Apr 2024 21:55:49 -0700
From: Shakeel Butt <shakeel.butt@linux.dev>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, 
	Josh Poimboeuf <jpoimboe@kernel.org>, Jeff Layton <jlayton@kernel.org>, 
	Chuck Lever <chuck.lever@oracle.com>, Kees Cook <kees@kernel.org>, Christoph Lameter <cl@linux.com>, 
	Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, 
	Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, 
	Roman Gushchin <roman.gushchin@linux.dev>, Hyeonggon Yoo <42.hyeyoo@gmail.com>, 
	Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, 
	Muchun Song <muchun.song@linux.dev>, Alexander Viro <viro@zeniv.linux.org.uk>, 
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org, 
	Chengming Zhou <chengming.zhou@linux.dev>
Subject: Re: [PATCH v2 1/2] mm, slab: move memcg charging to post-alloc hook
Message-ID: <sgzta3zm3os6nraxtb37affiz4itbz32qm2ceadh2wgwk6o33p@cenn36d6dqfa>
References: <20240325-slab-memcg-v2-0-900a458233a6@suse.cz>
 <20240325-slab-memcg-v2-1-900a458233a6@suse.cz>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240325-slab-memcg-v2-1-900a458233a6@suse.cz>

On Mon, Mar 25, 2024 at 09:20:32AM +0100, Vlastimil Babka wrote:
> The MEMCG_KMEM integration with slab currently relies on two hooks
> during allocation. memcg_slab_pre_alloc_hook() determines the objcg and
> charges it, and memcg_slab_post_alloc_hook() assigns the objcg pointer
> to the allocated object(s).
> 
> As Linus pointed out, this is unnecessarily complex. Failing to charge
> due to memcg limits should be rare, so we can optimistically allocate
> the object(s) and do the charging together with assigning the objcg
> pointer in a single post_alloc hook. In the rare case the charging
> fails, we can free the object(s) back.
> 
> This simplifies the code (no need to pass around the objcg pointer) and
> potentially allows to separate charging from allocation in cases where
> it's common that the allocation would be immediately freed, and the
> memcg handling overhead could be saved.
> 
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Link: https://lore.kernel.org/all/CAHk-=whYOOdM7jWy5jdrAm8LxcgCMFyk2bt8fYYvZzM4U-zAQA@mail.gmail.com/
> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
> Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>