linux-kernel - Re: [PATCH] memcg: decouple memcg_hotplug_cpu_dead from stock

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Message-ID: <atnweqyv7rnyzei3at2dm4xxca4ctvuod2w7brejg4b5zydgdm@xobzurjmjhy5>
Date: Mon, 14 Apr 2025 10:52:22 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>, Waiman Long <llong@...hat.com>, Vlastimil Babka <vbabka@...e.cz>, 
	linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: decouple memcg_hotplug_cpu_dead from stock_lock

(I was trying to reply last week but my email stopped working, so trying
again)

On Thu, Apr 10, 2025 at 10:06:18PM -0700, Andrew Morton wrote:
> On Thu, 10 Apr 2025 14:06:23 -0700 Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> 
> > The function memcg_hotplug_cpu_dead works on the stock of a remote dead
> > CPU and drain_obj_stock works on the given stock instead of local stock,
> > so there is no need to take local stock_lock anymore.
> > 
> > @@ -1964,10 +1964,10 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
> >  
> >  	stock = &per_cpu(memcg_stock, cpu);
> >  
> > -	/* drain_obj_stock requires stock_lock */
> > -	local_lock_irqsave(&memcg_stock.stock_lock, flags);
> > -	drain_obj_stock(stock);
> > -	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
> > +	local_irq_save(flag);
> > +	/* stock of a remote dead cpu, no need for stock_lock. */
> > +	__drain_obj_stock(stock);
> > +	local_irq_restore(flag);
> >  
> 
> s/flag/flags/
> 
> Obviously what-i-got isn't what-you-tested.  Please check what happened
> here,

Sorry about that. I tested the previous version where I had
drain_obj_stock() as a separate function but after seeing that there is
just one caller, I manually inlined it but forgot to test before
sending.