The quilt patch titled Subject: mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free has been removed from the -mm tree. Its filename was mm-page_alloc-make-percpu_pagelist_high_fraction-reads-lock-free.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------ From: Aboorva Devarajan aboorvad@linux.ibm.com Subject: mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free Date: Mon, 1 Dec 2025 11:30:09 +0530
When page isolation loops indefinitely during memory offline, reading /proc/sys/vm/percpu_pagelist_high_fraction blocks on pcp_batch_high_lock, causing hung task warnings.
Make procfs reads lock-free since percpu_pagelist_high_fraction is a simple integer with naturally atomic reads, writers still serialize via the mutex.
This prevents hung task warnings when reading the procfs file during long-running memory offline operations.
[akpm@linux-foundation.org: add comment, per Michal] Link: https://lkml.kernel.org/r/aS_y9AuJQFydLEXo@tiehlicka Link: https://lkml.kernel.org/r/20251201060009.1420792-1-aboorvad@linux.ibm.com Signed-off-by: Aboorva Devarajan aboorvad@linux.ibm.com Acked-by: Michal Hocko mhocko@suse.com Cc: Brendan Jackman jackmanb@google.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Suren Baghdasaryan surenb@google.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Zi Yan ziy@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/page_alloc.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/mm/page_alloc.c~mm-page_alloc-make-percpu_pagelist_high_fraction-reads-lock-free +++ a/mm/page_alloc.c @@ -6667,11 +6667,19 @@ static int percpu_pagelist_high_fraction int old_percpu_pagelist_high_fraction; int ret;
+ /* + * Avoid using pcp_batch_high_lock for reads as the value is read + * atomically and a race with offlining is harmless. + */ + + if (!write) + return proc_dointvec_minmax(table, write, buffer, length, ppos); + mutex_lock(&pcp_batch_high_lock); old_percpu_pagelist_high_fraction = percpu_pagelist_high_fraction;
ret = proc_dointvec_minmax(table, write, buffer, length, ppos); - if (!write || ret < 0) + if (ret < 0) goto out;
/* Sanity checking to avoid pcp imbalance */ _
Patches currently in -mm which might be from aboorvad@linux.ibm.com are