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mm/damon/sysfs: set damon_ctx->min_sz_region only for paddr use case

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damon_ctx->addr_unit is respected only for physical address space
monitoring use case.  Meanwhile, damon_ctx->min_sz_region is used by the
core layer for aligning regions, regardless of whether it is set for
physical address space monitoring or virtual address spaces monitoring. 
And it is set as 'DAMON_MIN_REGION / damon_ctx->addr_unit'.  Hence, if
user sets ->addr_unit on virtual address spaces monitoring mode, regions
can be unexpectedly aligned in <PAGE_SIZE granularity.  It shouldn't cause
crash-like issues but make monitoring and DAMOS behavior difficult to
understand.

Fix the unexpected behavior by setting ->min_sz_region only when it is
configured for physical address space monitoring.

The issue was found from a result of Chris' experiments that thankfully
shared with me off-list.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: d8f867fa08 ("mm/damon: add damon_ctx->min_sz_region")
Signed-off-by: SeongJae Park <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: ze zuo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
This commit is contained in:
SeongJae Park authored and Andrew Morton committed 2025-09-23 14:14:16 -07:00
1 parent 7ef5268a90
commit 8d009da32f
1 file changed
+4 -1
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mm/damon/sysfs.c
+4 -1
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@@ -1435,7 +1435,10 @@ static int damon_sysfs_apply_inputs(struct damon_ctx *ctx,
if (err)
return err;
ctx->addr_unit = sys_ctx->addr_unit;
ctx->min_sz_region = max(DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
/* addr_unit is respected by only DAMON_OPS_PADDR */
if (sys_ctx->ops_id == DAMON_OPS_PADDR)
ctx->min_sz_region = max(
DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
err = damon_sysfs_set_attrs(ctx, sys_ctx->attrs);
if (err)
return err;