linux-kernel - Re: [PATCH 2/9] memcg: decouple drain_obj

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z9jB2DFVY2R99ekS@google.com>
Date: Tue, 18 Mar 2025 00:44:08 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Vlastimil Babka <vbabka@...e.cz>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH 2/9] memcg: decouple drain_obj_stock from local stock

On Sat, Mar 15, 2025 at 10:49:23AM -0700, Shakeel Butt wrote:
> Currently drain_obj_stock() can potentially call __refill_stock which
> accesses local cpu stock and thus requires memcg stock's local_lock.
> However if we look at the code paths leading to drain_obj_stock(), there
> is never a good reason to refill the memcg stock at all from it.
> 
> At the moment, drain_obj_stock can be called from reclaim, hotplug cpu
> teardown, mod_objcg_state() and refill_obj_stock(). For reclaim and
> hotplug there is no need to refill. For the other two paths, most
> probably the newly switched objcg would be used in near future and thus
> no need to refill stock with the older objcg.
> 
> In addition, __refill_stock() from drain_obj_stock() happens on rare
> cases, so performance is not really an issue. Let's just uncharge
> directly instead of refill which will also decouple drain_obj_stock from
> local cpu stock and local_lock requirements.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Roman Gushchin <roman.gushchin@...ux.dev>