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Commit 398499d5 authored by Moussa A. Ba's avatar Moussa A. Ba Committed by Linus Torvalds
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pagemap clear_refs: modify to specify anon or mapped vma clearing 



The patch makes the clear_refs more versatile in adding the option to
select anonymous pages or file backed pages for clearing.  This addition
has a measurable impact on user space application performance as it
decreases the number of pagewalks in scenarios where one is only
interested in a specific type of page (anonymous or file mapped).

The patch adds anonymous and file backed filters to the clear_refs interface.

echo 1 > /proc/PID/clear_refs resets the bits on all pages
echo 2 > /proc/PID/clear_refs resets the bits on anonymous pages only
echo 3 > /proc/PID/clear_refs resets the bits on file backed pages only

Any other value is ignored

Signed-off-by: default avatarMoussa A. Ba <moussa.a.ba@gmail.com>
Signed-off-by: default avatarJared E. Hulbert <jaredeh@gmail.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7103ad32

Documentation/filesystems/proc.txt

+13 −0
Original line number Diff line number Diff line
@@ -375,6 +375,19 @@ of memory currently marked as referenced or accessed. 
This file is only present if the CONFIG_MMU kernel configuration option is

enabled.



The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG

bits on both physical and virtual pages associated with a process.

To clear the bits for all the pages associated with the process

    > echo 1 > /proc/PID/clear_refs



To clear the bits for the anonymous pages associated with the process

    > echo 2 > /proc/PID/clear_refs



To clear the bits for the file mapped pages associated with the process

    > echo 3 > /proc/PID/clear_refs

Any other value written to /proc/PID/clear_refs will have no effect.





1.2 Kernel data

---------------

fs/proc/task_mmu.c

+24 −4
Original line number Diff line number Diff line
@@ -465,6 +465,10 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr, 
	return 0;

}



#define CLEAR_REFS_ALL 1

#define CLEAR_REFS_ANON 2

#define CLEAR_REFS_MAPPED 3



static ssize_t clear_refs_write(struct file *file, const char __user *buf,

				size_t count, loff_t *ppos)

{
@@ -472,13 +476,15 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, 
	char buffer[PROC_NUMBUF], *end;

	struct mm_struct *mm;

	struct vm_area_struct *vma;

	int type;



	memset(buffer, 0, sizeof(buffer));

	if (count > sizeof(buffer) - 1)

		count = sizeof(buffer) - 1;

	if (copy_from_user(buffer, buf, count))

		return -EFAULT;

	if (!simple_strtol(buffer, &end, 0))

	type = simple_strtol(buffer, &end, 0);

	if (type < CLEAR_REFS_ALL || type > CLEAR_REFS_MAPPED)

		return -EINVAL;

	if (*end == '\n')

		end++;
@@ -494,7 +500,21 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, 
		down_read(&mm->mmap_sem);

		for (vma = mm->mmap; vma; vma = vma->vm_next) {

			clear_refs_walk.private = vma;

			if (!is_vm_hugetlb_page(vma))

			if (is_vm_hugetlb_page(vma))

				continue;

			/*

			 * Writing 1 to /proc/pid/clear_refs affects all pages.

			 *

			 * Writing 2 to /proc/pid/clear_refs only affects

			 * Anonymous pages.

			 *

			 * Writing 3 to /proc/pid/clear_refs only affects file

			 * mapped pages.

			 */

			if (type == CLEAR_REFS_ANON && vma->vm_file)

				continue;

			if (type == CLEAR_REFS_MAPPED && !vma->vm_file)

				continue;

			walk_page_range(vma->vm_start, vma->vm_end,

					&clear_refs_walk);

		}