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Message-ID: <alpine.DEB.2.00.0907271339070.17425@chino.kir.corp.google.com>
Date: Mon, 27 Jul 2009 13:57:36 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: "Moussa A. Ba" <moussa.a.ba@...il.com>
cc: linux-kernel@...r.kernel.org, xiyou.wangcong@...il.com,
Andrew Morton <akpm@...ux-foundation.org>,
Alexey Dobriyan <adobriyan@...il.com>,
Matt Mackall <mpm@...enic.com>, Mel Gorman <mel@....ul.ie>,
Ying Han <yinghan@...gle.com>, Nick Piggin <npiggin@...e.de>,
jaredeh@...il.com
Subject: Re: [PATCH 1/1] pagemap clear_refs: modify to specify anon or mapped
vma clearing
On Mon, 27 Jul 2009, Moussa A. Ba wrote:
> This patch makes the clear_refs proc interface a bit more versatile.
> It adds support for clearing anonymous pages, file mapped pages or both.
>
It already has support for clearing both, so you're only adding anonymous
and file-backed filters.
> The clear_refs entry is used to reset the Referenced bits on virtual and
> physical pages associated with a process.
> echo 1 > /proc/PID/clear_refs clears all pages associated with the process
> echo 2 > /proc/PID/clear_refs clears anonymous pages only
> echo 3 > /proc/PID/clear_refs clears file mapped pages only
> Any other value written to the proc entry will clear all pages.
>
clear_refs currently accepts any non-zero value, so it's possible that
this will break user scripts that, for whatever reason, write '2' or '3'.
I think that's acceptable, but it would be helpful to make all other
values a no-op similar to drop_caches at this point to avoid the potential
for breakage if this is ever extended any further.
> Selective clearing the pages has a measurable impact on performance as it
> limits the number of page walks. We have been using this interface and this
> adds flexibility to the user user space application implementing the reference
> clearing.
>
> Signed-off-by: Jared Hulbert (jaredeh@...il.com)
> Signed-off-by: Moussa A. Ba (moussa.a.ba@...il.com)
Email addresses in < > braces, please.
The first sign-off line normally indicates who wrote the patch, but your
submission lacks a From: line, so git would indicate you wrote it. If
that's incorrect, please add a From: line as described in
Documentation/SubmittingPatches. If it's correct, please reorder your
sign-off lines.
> -------
> Documentation/filesystems/proc.txt | 7 +++++++
> fs/proc/task_mmu.c | 29 +++++++++++++++++++++++++----
> 2 files changed, 32 insertions(+), 4 deletions(-)
>
> --- a/fs/proc/task_mmu.c 2009-07-21 14:30:01.000000000 -0700
> +++ b/fs/proc/task_mmu.c 2009-07-27 11:46:05.000000000 -0700
> @@ -462,6 +462,27 @@
> return 0;
> }
>
> +static void walk_vma_area(struct mm_walk *this_walk,
> + struct vm_area_struct *vma, int type)
> +{
This is a very generic name for something that is only applicable to
clear_refs, so please name it accordingly. This will also avoid having to
pass the struct mm_walk * in since its only user is clear_refs_walk.
> +
> + /* Writing 2 to /proc/pid/clear_refs will clear all Anonymous
> + * pages.
> + *
> + * Writing 3 to /proc/pid/clear_refs will clear all file mapped
> + * pages.
> + *
> + * Writing any other value including 1 will clear all pages
> + */
Documentation/CodingStyle would suggest this format:
/*
* Multi-line kernel comments always start ..
* with an empty first line.
*/
> + if (is_vm_hugetlb_page(vma))
> + return;
> + if (type == 2 && vma->vm_file)
> + return;
> + if (type == 3 && !vma->vm_file)
> + return;
> + walk_page_range(vma->vm_start, vma->vm_end, this_walk);
> +}
K&R would suggest #define's (or enums) for those hard-coded values. I
think that's already been suggested for this patch, actually.
> +
> static ssize_t clear_refs_write(struct file *file, const char __user * buf,
> size_t count, loff_t * ppos)
> {
> @@ -469,13 +490,15 @@
> 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 = strict_strtol(buffer, &end, 0);
> + if (!type)
> return -EINVAL;
> if (*end == '\n')
> end++;
> @@ -491,9 +514,7 @@
> 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))
> - walk_page_range(vma->vm_start, vma->vm_end,
> - &clear_refs_walk);
> + walk_vma_area(&clear_refs_walk, vma, type);
> }
> flush_tlb_mm(mm);
> up_read(&mm->mmap_sem);
> --- a/Documentation/filesystems/proc.txt 2009-07-20 17:29:11.000000000
> -0700
> +++ b/Documentation/filesystems/proc.txt 2009-07-27 12:08:34.000000000
> -0700
> @@ -375,6 +375,13 @@
> This file is only present if the CONFIG_MMU kernel configuration option is
> enabled.
>
> +The clear_refs entry is used to reset the Referenced bits on virtual and physical
> +pages associated with a process.
> +echo 1 > /proc/PID/clear_refs clears all pages associated with the process
> +echo 2 > /proc/PID/clear_refs clears anonymous pages only
> +echo 3 > /proc/PID/clear_refs clears file mapped pages only
> +Any other value written to the proc entry will clear all pages.
> +
Please follow the format in this document for how other /proc/PID/*
entries are described.
That format could really be improved here, perhaps you could clean
proc.txt up a little bit while you're here?
Also, as the author of clear_refs, please cc me on future revisions of
this patch.
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