mm/damon/schemes: account scheme actions that successfully applied

Patch series "mm/damon/schemes: Extend stats for better online analysis and tuning".

To help online access pattern analysis and tuning of DAMON-based
Operation Schemes (DAMOS), DAMOS provides simple statistics for each
scheme.  Introduction of DAMOS time/space quota further made the tuning
easier by making the risk management easier.  However, that also made
understanding of the working schemes a little bit more difficult.

For an example, progress of a given scheme can now be throttled by not
only the aggressiveness of the target access pattern, but also the
time/space quotas.  So, when a scheme is showing unexpectedly slow
progress, it's difficult to know by what the progress of the scheme is
throttled, with currently provided statistics.

This patchset extends the statistics to contain some metrics that can be
helpful for such online schemes analysis and tuning (patches 1-2),
exports those to users (patches 3 and 5), and add documents (patches 4
and 6).

This patch (of 6):

DAMON-based operation schemes (DAMOS) stats provide only the number and
the amount of regions that the action of the scheme has tried to be
applied.  Because the action could be failed for some reasons, the
currently provided information is sometimes not useful or convenient
enough for schemes profiling and tuning.  To improve this situation,
this commit extends the DAMOS stats to provide the number and the amount
of regions that the action has successfully applied.

Link: https://lkml.kernel.org/r/20211210150016.35349-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20211210150016.35349-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 32 insertions, 26 deletions

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 4515cf82c433..d745bf28509f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -102,8 +102,7 @@ struct damos *damon_new_scheme(
 	scheme->min_age_region = min_age_region;
 	scheme->max_age_region = max_age_region;
 	scheme->action = action;
-	scheme->stat_count = 0;
-	scheme->stat_sz = 0;
+	scheme->stat = (struct damos_stat){};
 	INIT_LIST_HEAD(&scheme->list);
 
 	scheme->quota.ms = quota->ms;
@@ -574,6 +573,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		struct damos_quota *quota = &s->quota;
 		unsigned long sz = r->ar.end - r->ar.start;
 		struct timespec64 begin, end;
+		unsigned long sz_applied = 0;
 
 		if (!s->wmarks.activated)
 			continue;
@@ -627,7 +627,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 				damon_split_region_at(c, t, r, sz);
 			}
 			ktime_get_coarse_ts64(&begin);
-			c->primitive.apply_scheme(c, t, r, s);
+			sz_applied = c->primitive.apply_scheme(c, t, r, s);
 			ktime_get_coarse_ts64(&end);
 			quota->total_charged_ns += timespec64_to_ns(&end) -
 				timespec64_to_ns(&begin);
@@ -641,8 +641,11 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 			r->age = 0;
 
 update_stat:
-		s->stat_count++;
-		s->stat_sz += sz;
+		s->stat.nr_tried++;
+		s->stat.sz_tried += sz;
+		if (sz_applied)
+			s->stat.nr_applied++;
+		s->stat.sz_applied += sz_applied;
 	}
 }
 
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index bf36a2756cfb..9318b52d0b46 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -117,7 +117,7 @@ static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
 				s->quota.weight_age,
 				s->wmarks.metric, s->wmarks.interval,
 				s->wmarks.high, s->wmarks.mid, s->wmarks.low,
-				s->stat_count, s->stat_sz);
+				s->stat.nr_tried, s->stat.sz_tried);
 		if (!rc)
 			return -ENOMEM;
 
diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 4318134cbc4c..5e8244f65a1a 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -213,14 +213,15 @@ bool damon_pa_target_valid(void *t)
 	return true;
 }
 
-static int damon_pa_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
-		struct damon_region *r, struct damos *scheme)
+static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
+		struct damon_target *t, struct damon_region *r,
+		struct damos *scheme)
 {
-	unsigned long addr;
+	unsigned long addr, applied;
 	LIST_HEAD(page_list);
 
 	if (scheme->action != DAMOS_PAGEOUT)
-		return -EINVAL;
+		return 0;
 
 	for (addr = r->ar.start; addr < r->ar.end; addr += PAGE_SIZE) {
 		struct page *page = damon_get_page(PHYS_PFN(addr));
@@ -241,9 +242,9 @@ static int damon_pa_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
 			put_page(page);
 		}
 	}
-	reclaim_pages(&page_list);
+	applied = reclaim_pages(&page_list);
 	cond_resched();
-	return 0;
+	return applied * PAGE_SIZE;
 }
 
 static int damon_pa_scheme_score(struct damon_ctx *context,
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 68d9e4134816..a10df3fd3d02 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -572,32 +572,34 @@ bool damon_va_target_valid(void *target)
 }
 
 #ifndef CONFIG_ADVISE_SYSCALLS
-static int damos_madvise(struct damon_target *target, struct damon_region *r,
-			int behavior)
+static unsigned long damos_madvise(struct damon_target *target,
+		struct damon_region *r, int behavior)
 {
-	return -EINVAL;
+	return 0;
 }
 #else
-static int damos_madvise(struct damon_target *target, struct damon_region *r,
-			int behavior)
+static unsigned long damos_madvise(struct damon_target *target,
+		struct damon_region *r, int behavior)
 {
 	struct mm_struct *mm;
-	int ret = -ENOMEM;
+	unsigned long start = PAGE_ALIGN(r->ar.start);
+	unsigned long len = PAGE_ALIGN(r->ar.end - r->ar.start);
+	unsigned long applied;
 
 	mm = damon_get_mm(target);
 	if (!mm)
-		goto out;
+		return 0;
 
-	ret = do_madvise(mm, PAGE_ALIGN(r->ar.start),
-			PAGE_ALIGN(r->ar.end - r->ar.start), behavior);
+	applied = do_madvise(mm, start, len, behavior) ? 0 : len;
 	mmput(mm);
-out:
-	return ret;
+
+	return applied;
 }
 #endif	/* CONFIG_ADVISE_SYSCALLS */
 
-static int damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
-		struct damon_region *r, struct damos *scheme)
+static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
+		struct damon_target *t, struct damon_region *r,
+		struct damos *scheme)
 {
 	int madv_action;
 
@@ -620,7 +622,7 @@ static int damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
 	case DAMOS_STAT:
 		return 0;
 	default:
-		return -EINVAL;
+		return 0;
 	}
 
 	return damos_madvise(t, r, madv_action);