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Message-ID: <ylswk3xbfulik5bumfsbnocnmdxez24qgoyh2dfi5nobfpxdvf@3dfbwepuztbb> Date: Fri, 6 Sep 2024 12:04:28 -0700 From: Shakeel Butt <shakeel.butt@...ux.dev> To: Vlastimil Babka <vbabka@...e.cz> Cc: Yosry Ahmed <yosryahmed@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, David Rientjes <rientjes@...gle.com>, Hyeonggon Yoo <42.hyeyoo@...il.com>, Eric Dumazet <edumazet@...gle.com>, "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Meta kernel team <kernel-team@...a.com>, cgroups@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH v4] memcg: add charging of already allocated slab objects On Fri, Sep 06, 2024 at 07:28:56PM GMT, Vlastimil Babka wrote: > On 9/6/24 19:19, Yosry Ahmed wrote: > > [..] > >> I felt it could be improved more, so ended up with this. Thoughts? > >> > >> /** > >> * kmem_cache_charge - memcg charge an already allocated slab memory > >> * @objp: address of the slab object to memcg charge > >> * @gfpflags: describe the allocation context > >> * > >> * kmem_cache_charge allows charging a slab object to the current memcg, > >> * primarily in cases where charging at allocation time might not be possible > >> * because the target memcg is not known (i.e. softirq context) > >> * > >> * The objp should be pointer returned by the slab allocator functions like > >> * kmalloc (with __GFP_ACCOUNT in flags) or kmem_cache_alloc. The memcg charge > > > > Aren't allocations done with kmalloc(__GFP_ACCOUNT) already accounted? > > Why would we need to call kmem_cache_charge() for those? > > AFAIU current_obj_cgroup() returns NULL because we're in the interrupt > context and no remote memcg context has been set. Thus the charging is > skipped. The patch commit log describes such scenario for network receive. > But in case of kmalloc() the allocation must have been still attempted with > __GFP_ACCOUNT so a kmalloc-cg cache is used even if the charging fails. > > If there's another usage for kmem_cache_charge() where the memcg is > available but we don't want to charge immediately on purpose (such as the > Linus' idea for struct file), we might need to find another way to tell > kmalloc() to use the kmalloc-cg cache but not charge immediately... > For the struct file, we already have a dedicated kmem_cache (filp_cachep), so no additional handling would be needed. However in future we might have cases where we want the kmalloc allocations to happen from non-normal kmalloc caches and then we can add mechanism to support such cases.
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