linux-kernel - Re: [PATCH] memcg: multi-memcg percpu charge cache

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: <20250422181022.308116c1@kernel.org>
Date: Tue, 22 Apr 2025 18:10:22 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: 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>, Vlastimil
 Babka <vbabka@...e.cz>, Eric Dumazet <edumazet@...gle.com>, Soheil Hassas
 Yeganeh <soheil@...gle.com>, linux-mm@...ck.org, cgroups@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Meta kernel team
 <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: multi-memcg percpu charge cache

On Wed, 16 Apr 2025 11:02:29 -0700 Shakeel Butt wrote:
>  static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
>  {
>  	struct memcg_stock_pcp *stock;
> -	unsigned int stock_pages;
> +	struct mem_cgroup *cached;
> +	uint8_t stock_pages;

Is it okay to use uintX_t now?

>  	unsigned long flags;
> +	bool evict = true;
> +	int i;
>  
>  	VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg));
>  
> -	if (!local_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
> +	if (nr_pages > MEMCG_CHARGE_BATCH ||
> +	    !local_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
>  		/*
> -		 * In case of unlikely failure to lock percpu stock_lock
> -		 * uncharge memcg directly.
> +		 * In case of larger than batch refill or unlikely failure to
> +		 * lock the percpu stock_lock, uncharge memcg directly.
>  		 */

We're bypassing the cache for > CHARGE_BATCH because the u8 math 
may overflow? Could be useful to refocus the comment on the 'why'

>  		memcg_uncharge(memcg, nr_pages);
>  		return;
>  	}

nits notwithstanding:

Acked-by: Jakub Kicinski <kuba@...nel.org>

Thanks!