From 0c75714095e06692f7a0e00a3dfd829c0d3c0ada Mon Sep 17 00:00:00 2001 From: Joshua Hahn Date: Thu, 18 Dec 2025 00:31:59 -0800 Subject: [PATCH] mm/page_alloc: report 1 as zone_batchsize for !CONFIG_MMU 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. Link: https://lkml.kernel.org/r/20251218083200.2435789-1-joshua.hahnjy@gmail.com Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") Signed-off-by: Joshua Hahn Reported-by: Daniel Palmer Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/ Reported-by: Guenter Roeck Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/ Reviewed-by: Vlastimil Babka Tested-by: Daniel Palmer Tested-by: Guenter Roeck Acked-by: SeongJae Park Tested-by: Hajime Tazaki Cc: Brendan Jackman Cc: Johannes Weiner Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index f6586f165b89..c380f063e8b7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5924,7 +5924,7 @@ static int zone_batchsize(struct zone *zone) * recycled, this leads to the once large chunks of space being * fragmented and becoming unavailable for high-order allocations. */ - return 0; + return 1; #endif }