mm/damon/schemes: add 'LRU_PRIO' DAMOS action

This commit adds a new DAMOS action called 'LRU_PRIO' for the physical
address space.  The action prioritizes pages in the memory regions of the
user-specified target access pattern on their LRU lists.  This is hence
supposed to be used for frequently accessed (hot) memory regions so that
hot pages could be more likely protected under memory pressure. 
Internally, it simply calls 'mark_page_accessed()'.

Link: https://lkml.kernel.org/r/20220613192301.8817-5-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/damon.h

@@ -86,6 +86,7 @@ struct damon_target {
  * @DAMOS_PAGEOUT:	Call ``madvise()`` for the region with MADV_PAGEOUT.
  * @DAMOS_HUGEPAGE:	Call ``madvise()`` for the region with MADV_HUGEPAGE.
  * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
+ * @DAMOS_LRU_PRIO:	Prioritize the region on its LRU lists.
  * @DAMOS_STAT:		Do nothing but count the stat.
  * @NR_DAMOS_ACTIONS:	Total number of DAMOS actions
  */
@@ -95,6 +96,7 @@ enum damos_action {
 	DAMOS_PAGEOUT,
 	DAMOS_HUGEPAGE,
 	DAMOS_NOHUGEPAGE,
+	DAMOS_LRU_PRIO,
 	DAMOS_STAT,		/* Do nothing but only record the stat */
 	NR_DAMOS_ACTIONS,
 };

mm/damon/ops-common.c

@@ -130,3 +130,45 @@ int damon_pageout_score(struct damon_ctx *c, struct damon_region *r,
 	/* Return coldness of the region */
 	return DAMOS_MAX_SCORE - hotness;
 }
+
+int damon_hot_score(struct damon_ctx *c, struct damon_region *r,
+			struct damos *s)
+{
+	unsigned int max_nr_accesses;
+	int freq_subscore;
+	unsigned int age_in_sec;
+	int age_in_log, age_subscore;
+	unsigned int freq_weight = s->quota.weight_nr_accesses;
+	unsigned int age_weight = s->quota.weight_age;
+	int hotness;
+
+	max_nr_accesses = c->aggr_interval / c->sample_interval;
+	freq_subscore = r->nr_accesses * DAMON_MAX_SUBSCORE / max_nr_accesses;
+
+	age_in_sec = (unsigned long)r->age * c->aggr_interval / 1000000;
+	for (age_in_log = 0; age_in_log < DAMON_MAX_AGE_IN_LOG && age_in_sec;
+			age_in_log++, age_in_sec >>= 1)
+		;
+
+	/* If frequency is 0, higher age means it's colder */
+	if (freq_subscore == 0)
+		age_in_log *= -1;
+
+	/*
+	 * Now age_in_log is in [-DAMON_MAX_AGE_IN_LOG, DAMON_MAX_AGE_IN_LOG].
+	 * Scale it to be in [0, 100] and set it as age subscore.
+	 */
+	age_in_log += DAMON_MAX_AGE_IN_LOG;
+	age_subscore = age_in_log * DAMON_MAX_SUBSCORE /
+		DAMON_MAX_AGE_IN_LOG / 2;
+
+	hotness = (freq_weight * freq_subscore + age_weight * age_subscore);
+	if (freq_weight + age_weight)
+		hotness /= freq_weight + age_weight;
+	/*
+	 * Transform it to fit in [0, DAMOS_MAX_SCORE]
+	 */
+	hotness = hotness * DAMOS_MAX_SCORE / DAMON_MAX_SUBSCORE;
+
+	return hotness;
+}

mm/damon/ops-common.h

@@ -14,3 +14,5 @@ void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr);
 
 int damon_pageout_score(struct damon_ctx *c, struct damon_region *r,
 			struct damos *s);
+int damon_hot_score(struct damon_ctx *c, struct damon_region *r,
+			struct damos *s);

mm/damon/paddr.c

@@ -233,6 +233,22 @@ static unsigned long damon_pa_pageout(struct damon_region *r)
 	return applied * PAGE_SIZE;
 }
 
+static unsigned long damon_pa_mark_accessed(struct damon_region *r)
+{
+	unsigned long addr, applied = 0;
+
+	for (addr = r->ar.start; addr < r->ar.end; addr += PAGE_SIZE) {
+		struct page *page = damon_get_page(PHYS_PFN(addr));
+
+		if (!page)
+			continue;
+		mark_page_accessed(page);
+		put_page(page);
+		applied++;
+	}
+	return applied * PAGE_SIZE;
+}
+
 static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 		struct damon_target *t, struct damon_region *r,
 		struct damos *scheme)
@@ -240,6 +256,8 @@ static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 	switch (scheme->action) {
 	case DAMOS_PAGEOUT:
 		return damon_pa_pageout(r);
+	case DAMOS_LRU_PRIO:
+		return damon_pa_mark_accessed(r);
 	default:
 		break;
 	}
@@ -253,6 +271,8 @@ static int damon_pa_scheme_score(struct damon_ctx *context,
 	switch (scheme->action) {
 	case DAMOS_PAGEOUT:
 		return damon_pageout_score(context, r, scheme);
+	case DAMOS_LRU_PRIO:
+		return damon_hot_score(context, r, scheme);
 	default:
 		break;
 	}

mm/damon/sysfs.c

@@ -762,6 +762,7 @@ static const char * const damon_sysfs_damos_action_strs[] = {
 	"pageout",
 	"hugepage",
 	"nohugepage",
+	"lru_prio",
 	"stat",
 };