The patch titled Subject: mm/damon/stat: change last_refresh_jiffies to a global variable has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-stat-change-last_refresh_jiffies-to-a-global-variable.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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

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------------------------------------------------------ From: Quanmin Yan yanquanmin1@huawei.com Subject: mm/damon/stat: change last_refresh_jiffies to a global variable Date: Thu, 30 Oct 2025 10:07:45 +0800

Patch series "mm/damon: fixes for the jiffies-related issues", v2.

On 32-bit systems, the kernel initializes jiffies to "-5 minutes" to make jiffies wrap bugs appear earlier. However, this may cause the time_before() series of functions to return unexpected values, resulting in DAMON not functioning as intended. Meanwhile, similar issues exist in some specific user operation scenarios.

This patchset addresses these issues. The first patch is about the DAMON_STAT module, and the second patch is about the core layer's sysfs.

This patch (of 2):

In DAMON_STAT's damon_stat_damon_call_fn(), time_before_eq() is used to avoid unnecessarily frequent stat update.

On 32-bit systems, the kernel initializes jiffies to "-5 minutes" to make jiffies wrap bugs appear earlier. However, this causes time_before_eq() in DAMON_STAT to unexpectedly return true during the first 5 minutes after boot on 32-bit systems (see [1] for more explanation, which fixes another jiffies-related issue before). As a result, DAMON_STAT does not update any monitoring results during that period, which becomes more confusing when DAMON_STAT_ENABLED_DEFAULT is enabled.

There is also an issue unrelated to the system's word size[2]: if the user stops DAMON_STAT just after last_refresh_jiffies is updated and restarts it after 5 seconds or a longer delay, last_refresh_jiffies will retain an older value, causing time_before_eq() to return false and the update to happen earlier than expected.

Fix these issues by making last_refresh_jiffies a global variable and initializing it each time DAMON_STAT is started.

Link: https://lkml.kernel.org/r/20251030020746.967174-2-yanquanmin1@huawei.com Link: https://lkml.kernel.org/r/20250822025057.1740854-1-ekffu200098@gmail.com [1] Link: https://lore.kernel.org/all/20251028143250.50144-1-sj@kernel.org/ [2] Fixes: fabdd1e911da ("mm/damon/stat: calculate and expose estimated memory bandwidth") Signed-off-by: Quanmin Yan yanquanmin1@huawei.com Suggested-by: SeongJae Park sj@kernel.org Reviewed-by: SeongJae Park sj@kernel.org Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: ze zuo zuoze1@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/damon/stat.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/mm/damon/stat.c~mm-damon-stat-change-last_refresh_jiffies-to-a-global-variable +++ a/mm/damon/stat.c @@ -46,6 +46,8 @@ MODULE_PARM_DESC(aggr_interval_us,

static struct damon_ctx *damon_stat_context;

+static unsigned long damon_stat_last_refresh_jiffies; + static void damon_stat_set_estimated_memory_bandwidth(struct damon_ctx *c) { struct damon_target *t; @@ -130,13 +132,12 @@ static void damon_stat_set_idletime_perc static int damon_stat_damon_call_fn(void *data) { struct damon_ctx *c = data; - static unsigned long last_refresh_jiffies;

/* avoid unnecessarily frequent stat update */ - if (time_before_eq(jiffies, last_refresh_jiffies + + if (time_before_eq(jiffies, damon_stat_last_refresh_jiffies + msecs_to_jiffies(5 * MSEC_PER_SEC))) return 0; - last_refresh_jiffies = jiffies; + damon_stat_last_refresh_jiffies = jiffies;

aggr_interval_us = c->attrs.aggr_interval; damon_stat_set_estimated_memory_bandwidth(c); @@ -210,6 +211,8 @@ static int damon_stat_start(void) err = damon_start(&damon_stat_context, 1, true); if (err) return err; + + damon_stat_last_refresh_jiffies = jiffies; call_control.data = damon_stat_context; return damon_call(damon_stat_context, &call_control); } _

Patches currently in -mm which might be from yanquanmin1@huawei.com are

mm-damon-stat-change-last_refresh_jiffies-to-a-global-variable.patch mm-damon-sysfs-change-next_update_jiffies-to-a-global-variable.patch mm-damon-add-a-min_sz_region-parameter-to-damon_set_region_biggest_system_ram_default.patch mm-damon-reclaim-use-min_sz_region-for-core-address-alignment-when-setting-regions.patch