[RFC PATCH 07/18] mm/damon/paddr: report filter-passed bytes back for DAMOS_STAT action

[SeongJae Park <sj@kernel.org>]

DAMOS_STAT action handling of paddr DAMON operations set implementation
is simply ignoring the filters, and therefore not reporting back the
filter-passed bytes.  Apply the filtrs and report back the information.

Before this change, DAMOS_STAT was doing nothing for DAMOS filters.
Hence users might see some performance regressions.  Such regression for
use cases where no filter is added to the scheme will be negligible,
since this change implementation avoid unnecessary filtering works if no
filter is installed.

For old users who were using DAMOS_STAT with filters, the regression
could be visible depending on the size of the region and the overhead of
the installed DAMOS filters.  But, because the filters were completely
ignored before in the use case, no real users would really depend on
such use case that makes no point.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/paddr.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 5944316a0b4c..b0c283808ba6 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -485,6 +485,39 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s,
 	return applied * PAGE_SIZE;
 }
 
+static bool damon_pa_scheme_has_filter(struct damos *s)
+{
+	struct damos_filter *f;
+
+	damos_for_each_filter(f, s)
+		return true;
+	return false;
+}
+
+static unsigned long damon_pa_stat(struct damon_region *r, struct damos *s,
+		unsigned long *sz_filter_passed)
+{
+	unsigned long addr;
+	LIST_HEAD(folio_list);
+
+	if (!damon_pa_scheme_has_filter(s))
+		return 0;
+
+	for (addr = r->ar.start; addr < r->ar.end; addr += PAGE_SIZE) {
+		struct folio *folio = damon_get_folio(PHYS_PFN(addr));
+
+		if (!folio)
+			continue;
+
+		if (damos_pa_filter_out(s, folio))
+			goto put_folio;
+		else
+			*sz_filter_passed += folio_size(folio);
+put_folio:
+		folio_put(folio);
+	}
+	return 0;
+}
 
 static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 		struct damon_target *t, struct damon_region *r,
@@ -501,7 +534,7 @@ static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 	case DAMOS_MIGRATE_COLD:
 		return damon_pa_migrate(r, scheme, sz_filter_passed);
 	case DAMOS_STAT:
-		break;
+		return damon_pa_stat(r, scheme, sz_filter_passed);
 	default:
 		/* DAMOS actions that not yet supported by 'paddr'. */
 		break;
-- 
2.39.5