linux/mm/damon/ops-common.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Common Primitives for Data Access Monitoring
 *
 * Author: SeongJae Park <sj@kernel.org>
 */

#include <linux/mmu_notifier.h>
#include <linux/page_idle.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>

#include "ops-common.h"

/*
 * Get an online page for a pfn if it's in the LRU list.  Otherwise, returns
 * NULL.
 *
 * The body of this function is stolen from the 'page_idle_get_folio()'.  We
 * steal rather than reuse it because the code is quite simple.
 */
struct folio *damon_get_folio(unsigned long pfn)
{
	struct page *page = pfn_to_online_page(pfn);
	struct folio *folio;

	if (!page)
		return NULL;

	folio = page_folio(page);
	if (!folio_test_lru(folio) || !folio_try_get(folio))
		return NULL;
	if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) {
		folio_put(folio);
		folio = NULL;
	}
	return folio;
}

void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr)
{
	pte_t pteval = ptep_get(pte);
	struct folio *folio;
	bool young = false;
	unsigned long pfn;

	if (likely(pte_present(pteval)))
		pfn = pte_pfn(pteval);
	else
		pfn = swp_offset_pfn(pte_to_swp_entry(pteval));

	folio = damon_get_folio(pfn);
	if (!folio)
		return;

	/*
	 * PFN swap PTEs, such as device-exclusive ones, that actually map pages
	 * are "old" from a CPU perspective. The MMU notifier takes care of any
	 * device aspects.
	 */
	if (likely(pte_present(pteval)))
		young |= ptep_test_and_clear_young(vma, addr, pte);
	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
	if (young)
		folio_set_young(folio);

	folio_set_idle(folio);
	folio_put(folio);
}

void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));

	if (!folio)
		return;

	if (pmdp_clear_young_notify(vma, addr, pmd))
		folio_set_young(folio);

	folio_set_idle(folio);
	folio_put(folio);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
}

#define DAMON_MAX_SUBSCORE	(100)
#define DAMON_MAX_AGE_IN_LOG	(32)

int damon_hot_score(struct damon_ctx *c, struct damon_region *r,
			struct damos *s)
{
	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;

	freq_subscore = r->nr_accesses * DAMON_MAX_SUBSCORE /
		damon_max_nr_accesses(&c->attrs);

	age_in_sec = (unsigned long)r->age * c->attrs.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;
}

int damon_cold_score(struct damon_ctx *c, struct damon_region *r,
			struct damos *s)
{
	int hotness = damon_hot_score(c, r, s);

	/* Return coldness of the region */
	return DAMOS_MAX_SCORE - hotness;
}