Re: [PATCH] mm/damon/stat: monitor all System RAM resources

[SeongJae Park <sj@kernel.org>]

On Fri, 13 Mar 2026 16:40:22 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Thu, 12 Mar 2026 21:44:47 -0700 SeongJae Park <sj@kernel.org> wrote:
> 
> > DAMON_STAT usage document (Documentation/admin-guide/mm/damon/stat.rst)
> > says it monitors the system's entire physical memory.  But, it is
> > monitoring only the biggest System RAM resource of the system.  When
> > there are multiple System RAM resources, this results in monitoring only
> > an unexpectedly small fraction of the physical memory.  For example,
> > suppose the system has a 500 GiB System RAM, 10 MiB non-System RAM, and
> > 500 GiB System RAM resources in order on the physical address space.
> > DAMON_STAT will monitor only the first 500 GiB System RAM.  This
> > situation is particularly common on NUMA systems.
> > 
> > Select a physical address range that covers all System RAM areas of the
> > system, to fix this issue and make it work as documented.
> > 
> > Fixes: 369c415e6073 ("mm/damon: introduce DAMON_STAT module")
> > Cc: <stable@vger.kernel.org> # 6.17.x
> > Signed-off-by: SeongJae Park <sj@kernel.org>
> > ---
> >  mm/damon/stat.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 48 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/damon/stat.c b/mm/damon/stat.c
> > index f9a2028483b05..3ed71db33e899 100644
> > --- a/mm/damon/stat.c
> > +++ b/mm/damon/stat.c
> > @@ -145,12 +145,57 @@ static int damon_stat_damon_call_fn(void *data)
> >  	return 0;
> >  }
> >  
> > +struct damon_stat_system_ram_range_walk_arg {
> > +	bool walked;
> > +	struct resource res;
> > +};
> > +
> > +static int damon_stat_system_ram_walk_fn(struct resource *res, void *arg)
> > +{
> > +	struct damon_stat_system_ram_range_walk_arg *a = arg;
> > +
> > +	if (!a->walked) {
> > +		a->walked = true;
> > +		a->res.start = res->start;
> > +	}
> > +	a->res.end = res->end;
> > +	return 0;
> > +}
> > +
> > +static unsigned long damon_stat_res_to_core_addr(resource_size_t ra,
> > +		unsigned long addr_unit)
> > +{
> > +	/*
> > +	 * Use div_u64() for avoiding linking errors related with __udivdi3,
> > +	 * __aeabi_uldivmod, or similar problems.  This should also improve the
> > +	 * performance optimization (read div_u64() comment for the detail).
> > +	 */
> > +	if (sizeof(ra) == 8 && sizeof(addr_unit) == 4)
> > +		return div_u64(ra, addr_unit);
> > +	return ra / addr_unit;
> > +}
> > +
> > +static int damon_stat_set_monitoring_region(struct damon_target *t,
> > +		unsigned long addr_unit, unsigned long min_region_sz)
> > +{
> > +	struct damon_addr_range addr_range;
> > +	struct damon_stat_system_ram_range_walk_arg arg = {};
> > +
> > +	walk_system_ram_res(0, -1, &arg, damon_stat_system_ram_walk_fn);
> > +	if (!arg.walked)
> > +		return -EINVAL;
> > +	addr_range.start = damon_stat_res_to_core_addr(
> > +			arg.res.start, addr_unit);
> > +	addr_range.end = damon_stat_res_to_core_addr(
> > +			arg.res.end + 1, addr_unit);
> > +	return damon_set_regions(t, &addr_range, addr_unit, min_region_sz);
> 
> The third argument of damon_set_regions() is the number of ranges (length of
> the array passed by the second argument), so '1' should be passed.  But the
> patch is passing 'addr_unit'.  It will not cause a real issue since the value
> is set to '1' in this case.  But it is an obvious bug.  I will fix this in the
> v2.

Or, Andrew, if you prefer to, please pick below attaching fixup together.  I
will post v2 on Sunday if this is not picked up with the below fixup by
tomorrow.


Thanks,
SJ

[...]
=== >8 ===
From e5f029441de038289320a7cb99a249800d99471f Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Fri, 13 Mar 2026 16:41:00 -0700
Subject: [PATCH] mm/damon/stat: fix wrong argument to damon_set_regions()

The third argument for damon_set_regions() is the number of ranges in
the second argument, but the code is wrongly passing addr_unit.  Fix it.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/stat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/damon/stat.c b/mm/damon/stat.c
index 3ed71db33e899..c5af8ad4bcb65 100644
--- a/mm/damon/stat.c
+++ b/mm/damon/stat.c
@@ -188,7 +188,7 @@ static int damon_stat_set_monitoring_region(struct damon_target *t,
 			arg.res.start, addr_unit);
 	addr_range.end = damon_stat_res_to_core_addr(
 			arg.res.end + 1, addr_unit);
-	return damon_set_regions(t, &addr_range, addr_unit, min_region_sz);
+	return damon_set_regions(t, &addr_range, 1, min_region_sz);
 }
 
 static struct damon_ctx *damon_stat_build_ctx(void)
-- 
2.47.3