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// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/memblock.h>
#include <linux/fs.h>
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/memory_hotplug.h>
#include <linux/mm.h>
#include <linux/mmzone.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/page_ext.h>
#include <linux/page_idle.h>
#include "internal.h"
#define BITMAP_CHUNK_SIZE sizeof(u64)
#define BITMAP_CHUNK_BITS (BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
/*
* Idle page tracking only considers user memory pages, for other types of
* pages the idle flag is always unset and an attempt to set it is silently
* ignored.
*
* We treat a page as a user memory page if it is on an LRU list, because it is
* always safe to pass such a page to rmap_walk(), which is essential for idle
* page tracking. With such an indicator of user pages we can skip isolated
* pages, but since there are not usually many of them, it will hardly affect
* the overall result.
*
* This function tries to get a user memory page by pfn as described above.
*/
static struct folio *page_idle_get_folio(unsigned long pfn)
{
struct page *page = pfn_to_online_page(pfn);
struct folio *folio;
if (!page || PageTail(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;
}
static bool page_idle_clear_pte_refs_one(struct folio *folio,
struct vm_area_struct *vma,
unsigned long addr, void *arg)
{
DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, addr, 0);
bool referenced = false;
while (page_vma_mapped_walk(&pvmw)) {
addr = pvmw.address;
if (pvmw.pte) {
/*
* For PTE-mapped THP, one sub page is referenced,
* the whole THP is referenced.
*/
if (ptep_clear_young_notify(vma, addr, pvmw.pte))
referenced = true;
} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
referenced = true;
} else {
/* unexpected pmd-mapped page? */
WARN_ON_ONCE(1);
}
}
if (referenced) {
folio_clear_idle(folio);
/*
* We cleared the referenced bit in a mapping to this page. To
* avoid interference with page reclaim, mark it young so that
* folio_referenced() will return > 0.
*/
folio_set_young(folio);
}
return true;
}
static void page_idle_clear_pte_refs(struct folio *folio)
{
/*
* Since rwc.try_lock is unused, rwc is effectively immutable, so we
* can make it static to save some cycles and stack.
*/
static struct rmap_walk_control rwc = {
.rmap_one = page_idle_clear_pte_refs_one,
.anon_lock = folio_lock_anon_vma_read,
};
bool need_lock;
if (!folio_mapped(folio) || !folio_raw_mapping(folio))
return;
need_lock = !folio_test_anon(folio) || folio_test_ksm(folio);
if (need_lock && !folio_trylock(folio))
return;
rmap_walk(folio, &rwc);
if (need_lock)
folio_unlock(folio);
}
static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
struct bin_attribute *attr, char *buf,
loff_t pos, size_t count)
{
u64 *out = (u64 *)buf;
struct folio *folio;
unsigned long pfn, end_pfn;
int bit;
if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
return -EINVAL;
pfn = pos * BITS_PER_BYTE;
if (pfn >= max_pfn)
return 0;
end_pfn = pfn + count * BITS_PER_BYTE;
if (end_pfn > max_pfn)
end_pfn = max_pfn;
for (; pfn < end_pfn; pfn++) {
bit = pfn % BITMAP_CHUNK_BITS;
if (!bit)
*out = 0ULL;
folio = page_idle_get_folio(pfn);
if (folio) {
if (folio_test_idle(folio)) {
/*
* The page might have been referenced via a
* pte, in which case it is not idle. Clear
* refs and recheck.
*/
page_idle_clear_pte_refs(folio);
if (folio_test_idle(folio))
*out |= 1ULL << bit;
}
folio_put(folio);
}
if (bit == BITMAP_CHUNK_BITS - 1)
out++;
cond_resched();
}
return (char *)out - buf;
}
static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
struct bin_attribute *attr, char *buf,
loff_t pos, size_t count)
{
const u64 *in = (u64 *)buf;
struct folio *folio;
unsigned long pfn, end_pfn;
int bit;
if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
return -EINVAL;
pfn = pos * BITS_PER_BYTE;
if (pfn >= max_pfn)
return -ENXIO;
end_pfn = pfn + count * BITS_PER_BYTE;
if (end_pfn > max_pfn)
end_pfn = max_pfn;
for (; pfn < end_pfn; pfn++) {
bit = pfn % BITMAP_CHUNK_BITS;
if ((*in >> bit) & 1) {
folio = page_idle_get_folio(pfn);
if (folio) {
page_idle_clear_pte_refs(folio);
folio_set_idle(folio);
folio_put(folio);
}
}
if (bit == BITMAP_CHUNK_BITS - 1)
in++;
cond_resched();
}
return (char *)in - buf;
}
static struct bin_attribute page_idle_bitmap_attr =
__BIN_ATTR(bitmap, 0600,
page_idle_bitmap_read, page_idle_bitmap_write, 0);
static struct bin_attribute *page_idle_bin_attrs[] = {
&page_idle_bitmap_attr,
NULL,
};
static const struct attribute_group page_idle_attr_group = {
.bin_attrs = page_idle_bin_attrs,
.name = "page_idle",
};
static int __init page_idle_init(void)
{
int err;
err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
if (err) {
pr_err("page_idle: register sysfs failed\n");
return err;
}
return 0;
}
subsys_initcall(page_idle_init);
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