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mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free

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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>
This commit is contained in:
Aboorva Devarajan
2025-12-01 11:30:09 +05:30
committed by Andrew Morton
parent a38be54626
commit b9efe36b5e
1 changed files with 9 additions and 1 deletions
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10
mm/page_alloc.c
View File

@@ -6667,11 +6667,19 @@ static int percpu_pagelist_high_fraction_sysctl_handler(const struct ctl_table *
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 */