linux-kernel - Re: [PATCH] mm/page_alloc: restore 0-handling to zone_set_pageset_high_and

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Message-ID: <db40ce77-4762-4d99-b03a-439c977ba1b8@roeck-us.net>
Date: Wed, 17 Dec 2025 08:47:12 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Palmer <daniel@...f.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/page_alloc: restore 0-handling to
 zone_set_pageset_high_and_batch

On Tue, Dec 16, 2025 at 10:05:03PM -0800, Joshua Hahn wrote:
> Commit 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0")
> moved the error handling (0-handling) of zone_batchsize from its
> callers to inside the function. However, the commit left out the error
> handling for the NOMMU case, leading to deadlocks on NOMMU systems.
> 
> Since in the NOMMU case the reported-to-user batchsize should still be 0,
> we would only like the error handling to exist in the callsites that
> set the internal value for the zone (i.e. zone_set_pageset_high_and_batch).
> 
> Restore max(1, zone_batchsize(zone)) to the callsite to prevent errors
> on NOMMU systems.
> 
> Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0")
> Reported-by: Daniel Palmer <daniel@...ngy.jp>
> Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/
> Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>

For m68k:mcf5208evb boot tests with qemu:

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter