When setting regions in DAMON_RECLAIM, DAMON_MIN_REGION will be applied
as the core address alignment, and the monitoring target address ranges
would be aligned on DAMON_MIN_REGION * addr_unit. When users 1) set
addr_unit to a value larger than 1, and 2) set the monitoring target
address range as not aligned on DAMON_MIN_REGION * addr_unit, it will
cause DAMON_RECLAIM to operate on unexpectedly large physical address
ranges.

For example, if the user sets the monitoring target address range to
[4, 8) and addr_unit as 1024, the aimed monitoring target address range
is [4 KiB, 8 KiB). Assuming DAMON_MIN_REGION is 4096, so resulting
target address range will be [0, 4096) in the DAMON core layer address
system, and [0, 4 MiB) in the physical address space, which is an
unexpected range.

To fix the issue, use min_sz_region for core address alignment when
setting regions.

Fixes: 7db551fcfb2a ("mm/damon/reclaim: support addr_unit for DAMON_RECLAIM")
Signed-off-by: Quanmin Yan <yanquanmin1@huawei.com>
---
 mm/damon/reclaim.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index e30811cafe90..36a582e09eae 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -251,7 +251,7 @@ static int damon_reclaim_apply_parameters(void)
 	err = damon_set_region_biggest_system_ram_default(param_target,
 					&monitor_region_start,
 					&monitor_region_end,
-					DAMON_MIN_REGION);
+					param_ctx->min_sz_region);
 	if (err)
 		goto out;
 	err = damon_commit_ctx(ctx, param_ctx);
-- 
2.43.0

On Mon, 20 Oct 2025 21:01:25 +0800 Quanmin Yan <yanquanmin1@huawei.com> wrote:

> When setting regions in DAMON_RECLAIM, DAMON_MIN_REGION will be applied
> as the core address alignment, and the monitoring target address ranges
> would be aligned on DAMON_MIN_REGION * addr_unit. When users 1) set
> addr_unit to a value larger than 1, and 2) set the monitoring target
> address range as not aligned on DAMON_MIN_REGION * addr_unit, it will
> cause DAMON_RECLAIM to operate on unexpectedly large physical address
> ranges.
> 
> For example, if the user sets the monitoring target address range to
> [4, 8) and addr_unit as 1024, the aimed monitoring target address range
> is [4 KiB, 8 KiB). Assuming DAMON_MIN_REGION is 4096, so resulting
> target address range will be [0, 4096) in the DAMON core layer address
> system, and [0, 4 MiB) in the physical address space, which is an
> unexpected range.
> 
> To fix the issue, use min_sz_region for core address alignment when
> setting regions.
> 
> Fixes: 7db551fcfb2a ("mm/damon/reclaim: support addr_unit for DAMON_RECLAIM")
> Signed-off-by: Quanmin Yan <yanquanmin1@huawei.com>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

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