+ mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch added to mm-unstable branch

+ mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/page_alloc: only update lowmem_reserve_ratio on sysctl write
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Jianlin Shi <shijianlin11@foxmail.com>
Subject: mm/page_alloc: only update lowmem_reserve_ratio on sysctl write
Date: Sun, 2 Aug 2026 22:57:07 +0800

lowmem_reserve_ratio_sysctl_handler() ignores the return value of
proc_dointvec_minmax() and always calls setup_per_zone_lowmem_reserve(),
even for read operations.

Fix three issues:

1. Propagate errors from proc_dointvec_minmax() instead of always
   returning success.  For example, writing non-integer garbage to the
   sysctl now returns an error instead of silently succeeding with
   unchanged values.

2. Only call setup_per_zone_lowmem_reserve() when the sysctl is
   actually written, matching the write-only refresh pattern of
   min_free_kbytes and watermark_scale_factor handlers.

3. On write, parse into a temporary ratio[] array and only copy into
   sysctl_lowmem_reserve_ratio[] and refresh derived state after the
   full vector is validated.  This avoids leaving the ratio array
   partially updated while skipping setup when proc_dointvec_minmax()
   returns an error on a later element (suggested by Andrew Morton).

Drop the manual "< 1 -> 0" sanitization loop and set .extra1 =
SYSCTL_ZERO on the ctl_table entry so proc_dointvec_minmax() enforces
the minimum on write; negative values now return -EINVAL instead of
being silently coerced to 0 (suggested by Vlastimil Babka).

Link: https://lore.kernel.org/tencent_B9556590D4B65ACF74C06897689A6E39F206@qq.com
Link: https://lore.kernel.org/linux-mm/tencent_FFD4F4D728AAE8A8AE0AF277A59854A29A06@qq.com/
Signed-off-by: Jianlin Shi <shijianlin11@foxmail.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write
+++ a/mm/page_alloc.c
@@ -6915,8 +6915,8 @@ static int sysctl_min_slab_ratio_sysctl_
 
 /*
  * lowmem_reserve_ratio_sysctl_handler - just a wrapper around
- *	proc_dointvec() so that we can call setup_per_zone_lowmem_reserve()
- *	whenever sysctl_lowmem_reserve_ratio changes.
+ *	proc_dointvec_minmax() so that we can call
+ *	setup_per_zone_lowmem_reserve() when the sysctl is written.
  *
  * The reserve ratio obviously has absolutely no relation with the
  * minimum watermarks. The lowmem reserve ratio can only make sense
@@ -6925,16 +6925,23 @@ static int sysctl_min_slab_ratio_sysctl_
 static int lowmem_reserve_ratio_sysctl_handler(const struct ctl_table *table,
 		int write, void *buffer, size_t *length, loff_t *ppos)
 {
-	int i;
+	struct ctl_table tmp = *table;
+	int ratio[MAX_NR_ZONES];
+	int rc;
 
-	proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (!write)
+		return proc_dointvec_minmax(table, write, buffer, length, ppos);
 
-	for (i = 0; i < MAX_NR_ZONES; i++) {
-		if (sysctl_lowmem_reserve_ratio[i] < 1)
-			sysctl_lowmem_reserve_ratio[i] = 0;
-	}
+	memcpy(ratio, sysctl_lowmem_reserve_ratio, sizeof(ratio));
+	tmp.data = ratio;
 
+	rc = proc_dointvec_minmax(&tmp, write, buffer, length, ppos);
+	if (rc)
+		return rc;
+
+	memcpy(sysctl_lowmem_reserve_ratio, ratio, sizeof(ratio));
 	setup_per_zone_lowmem_reserve();
+
 	return 0;
 }
 
@@ -7033,6 +7040,7 @@ static const struct ctl_table page_alloc
 		.maxlen		= sizeof(sysctl_lowmem_reserve_ratio),
 		.mode		= 0644,
 		.proc_handler	= lowmem_reserve_ratio_sysctl_handler,
+		.extra1		= SYSCTL_ZERO,
 	},
 #ifdef CONFIG_NUMA
 	{
_

Patches currently in -mm which might be from shijianlin11@foxmail.com are

mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch
ipc-only-destroy-orphaned-shm-segments-on-sysctl-write.patch

+ mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/page_alloc: only update lowmem_reserve_ratio on sysctl write
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Jianlin Shi <shijianlin11@foxmail.com>
Subject: mm/page_alloc: only update lowmem_reserve_ratio on sysctl write
Date: Thu, 6 Aug 2026 16:27:34 +0800

lowmem_reserve_ratio_sysctl_handler() ignores the return value of
proc_dointvec_minmax() and always calls setup_per_zone_lowmem_reserve(),
even for read operations.

Fix three issues:

1. Propagate errors from proc_dointvec_minmax() instead of always
   returning success.  For example, writing non-integer garbage to the
   sysctl now returns an error instead of silently succeeding with
   unchanged values.

2. Only call setup_per_zone_lowmem_reserve() when the sysctl is
   actually written, matching the write-only refresh pattern of
   min_free_kbytes and watermark_scale_factor handlers.

3. On write, parse into a temporary ratio[] array and only copy into
   sysctl_lowmem_reserve_ratio[] and refresh derived state after the
   full vector is validated.  This avoids leaving the ratio array
   partially updated while skipping setup when proc_dointvec_minmax()
   returns an error on a later element (suggested by Andrew Morton).

Drop the manual "< 1 -> 0" sanitization loop and set .extra1 = SYSCTL_ZERO
on the ctl_table entry so proc_dointvec_minmax() enforces the minimum on
write; negative values now return -EINVAL instead of being silently
coerced to 0 (suggested by Vlastimil Babka).

Link: https://lore.kernel.org/linux-mm/tencent_FFD4F4D728AAE8A8AE0AF277A59854A29A06@qq.com/
Link: https://lore.kernel.org/tencent_A860C873956A52E26AD8D309A308A241BA08@qq.com
Signed-off-by: Jianlin Shi <shijianlin11@foxmail.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joel Granados <joel.granados@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write
+++ a/mm/page_alloc.c
@@ -6915,8 +6915,8 @@ static int sysctl_min_slab_ratio_sysctl_
 
 /*
  * lowmem_reserve_ratio_sysctl_handler - just a wrapper around
- *	proc_dointvec() so that we can call setup_per_zone_lowmem_reserve()
- *	whenever sysctl_lowmem_reserve_ratio changes.
+ *	proc_dointvec_minmax() so that we can call
+ *	setup_per_zone_lowmem_reserve() when the sysctl is written.
  *
  * The reserve ratio obviously has absolutely no relation with the
  * minimum watermarks. The lowmem reserve ratio can only make sense
@@ -6925,16 +6925,23 @@ static int sysctl_min_slab_ratio_sysctl_
 static int lowmem_reserve_ratio_sysctl_handler(const struct ctl_table *table,
 		int write, void *buffer, size_t *length, loff_t *ppos)
 {
-	int i;
+	struct ctl_table tmp = *table;
+	int ratio[ARRAY_SIZE(sysctl_lowmem_reserve_ratio)];
+	int rc;
 
-	proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (!write)
+		return proc_dointvec_minmax(table, write, buffer, length, ppos);
 
-	for (i = 0; i < MAX_NR_ZONES; i++) {
-		if (sysctl_lowmem_reserve_ratio[i] < 1)
-			sysctl_lowmem_reserve_ratio[i] = 0;
-	}
+	memcpy(ratio, sysctl_lowmem_reserve_ratio, sizeof(ratio));
+	tmp.data = ratio;
 
+	rc = proc_dointvec_minmax(&tmp, write, buffer, length, ppos);
+	if (rc)
+		return rc;
+
+	memcpy(sysctl_lowmem_reserve_ratio, ratio, sizeof(ratio));
 	setup_per_zone_lowmem_reserve();
+
 	return 0;
 }
 
@@ -7033,6 +7040,7 @@ static const struct ctl_table page_alloc
 		.maxlen		= sizeof(sysctl_lowmem_reserve_ratio),
 		.mode		= 0644,
 		.proc_handler	= lowmem_reserve_ratio_sysctl_handler,
+		.extra1		= SYSCTL_ZERO,
 	},
 #ifdef CONFIG_NUMA
 	{
_

Patches currently in -mm which might be from shijianlin11@foxmail.com are

mm-page_alloc-only-update-lowmem_reserve_ratio-on-sysctl-write.patch
ipc-only-destroy-orphaned-shm-segments-on-sysctl-write.patch