linux-kernel - Re: [PATCH 2/2] task_mmu: Add user-space support for resetting mm->hiwater

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Date:	Wed, 17 Dec 2014 14:30:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Petr Cermak <petrcermak@...omium.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Primiano Tucci <primiano@...omium.org>
Subject: Re: [PATCH 2/2] task_mmu: Add user-space support for resetting
 mm->hiwater_rss (peak RSS)

On Mon, 15 Dec 2014 17:15:33 +0000 Petr Cermak <petrcermak@...omium.org> wrote:

> Peak resident size of a process can be reset by writing "5" to
> /proc/pid/clear_refs. The driving use-case for this would be getting the
> peak RSS value, which can be retrieved from the VmHWM field in
> /proc/pid/status, per benchmark iteration or test scenario.

The term "reset" is ambiguous - it often means "reset it to zero".

This?

--- a/Documentation/filesystems/proc.txt~task_mmu-add-user-space-support-for-resetting-mm-hiwater_rss-peak-rss-fix
+++ a/Documentation/filesystems/proc.txt
@@ -488,7 +488,8 @@ To clear the bits for the file mapped pa
 To clear the soft-dirty bit
     > echo 4 > /proc/PID/clear_refs
 
-To reset the peak resident set size ("high water mark")
+To reset the peak resident set size ("high water mark") to the process's
+current value:
     > echo 5 > /proc/PID/clear_refs
 
 Any other value written to /proc/PID/clear_refs will have no effect.
--- a/fs/proc/task_mmu.c~task_mmu-add-user-space-support-for-resetting-mm-hiwater_rss-peak-rss-fix
+++ a/fs/proc/task_mmu.c
@@ -859,7 +859,7 @@ static ssize_t clear_refs_write(struct f
 	if (type == CLEAR_REFS_MM_HIWATER_RSS) {
 		/*
 		 * Writing 5 to /proc/pid/clear_refs resets the peak resident
-		 * set size.
+		 * set size to this mm's current rss value.
 		 */
 		down_write(&mm->mmap_sem);
 		reset_mm_hiwater_rss(mm);
_

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