linux-kernel - Re: [PATCH v2] sched_ext: Use kvzalloc for large exit

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Message-ID: <Z_Ugy6NDFBscP9Ef@gpd3>
Date: Tue, 8 Apr 2025 15:12:43 +0200
From: Andrea Righi <arighi@...dia.com>
To: Breno Leitao <leitao@...ian.org>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, christophe.jaillet@...adoo.fr,
	kernel-team@...a.com, stable@...r.kernel.org,
	Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v2] sched_ext: Use kvzalloc for large exit_dump allocation

On Tue, Apr 08, 2025 at 05:17:16AM -0700, Breno Leitao wrote:
> Hello Andrea,
> 
> On Tue, Apr 08, 2025 at 01:30:32PM +0200, Andrea Righi wrote:
> > Hi Breno,
> > 
> > I already acked even the buggy version, so this one looks good. :)
> > 
> > On Tue, Apr 08, 2025 at 04:09:02AM -0700, Breno Leitao wrote:
> > > Replace kzalloc with kvzalloc for the exit_dump buffer allocation, which
> > > can require large contiguous memory (up to order=9) depending on the
> > 
> > BTW, from where this order=9 is coming from? exit_dump_len is 32K by
> > default, but a BPF scheduler can arbitrarily set it to any value via
> > ops->exit_dump_len, so it could be even bigger than an order 9 allocation.
> 
> You are absolutely correct, this allocation could be of any size.
> 
> I've got this problem because I was monitoring the Meta fleet, and saw
> a bunch of allocation failures and decided to investigate. In this case
> specifically, the users were using order=9 (512 pages), but, again, this
> could be even bigger.

I see, makes sense. Maybe we can rephrase this part to not mention the
order=9 allocation and avoid potential confusion.

Thanks,
-Andrea