Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG_MMU

[Guenter Roeck]

On Thu, Dec 18, 2025 at 12:31:59AM -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.
> 
> For NOMMU systems, return 1 instead of 0 for zone_batchsize, which restores
> the previous deadlock-free behavior.
> 
> There is no functional difference expected with this patch before commit
> 2783088ef24e, other than the pr_debug in zone_pcp_init now printing out
> 1 instead of 0 for zones in NOMMU systems. Not only is this a pr_debug,
> the difference is purely semantic anyways.
> 
> Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0")
> Reported-by: Daniel Palmer <daniel@xxxxxxxxx>
> Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@xxxxxxxxxxxxxx/
> Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@xxxxxxxxxxxx/
> Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

Guenter