linux-kernel - Re: [PATCH -mm v8 7/7] proc: export idle flag via kpageflags

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Date:	Wed, 15 Jul 2015 12:17:02 -0700
From:	Andres Lagar-Cavilla <andreslc@...gle.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Jonathan Corbet <corbet@....net>, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v8 7/7] proc: export idle flag via kpageflags

On Wed, Jul 15, 2015 at 6:54 AM, Vladimir Davydov
<vdavydov@...allels.com> wrote:
> As noted by Minchan, a benefit of reading idle flag from
> /proc/kpageflags is that one can easily filter dirty and/or unevictable
> pages while estimating the size of unused memory.
>
> Note that idle flag read from /proc/kpageflags may be stale in case the
> page was accessed via a PTE, because it would be too costly to iterate
> over all page mappings on each /proc/kpageflags read to provide an
> up-to-date value. To make sure the flag is up-to-date one has to read
> /proc/kpageidle first.
>
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

Reviewed-by: Andres Lagar-Cavilla <andreslc@...gle.com>

> ---
>  Documentation/vm/pagemap.txt           | 6 ++++++
>  fs/proc/page.c                         | 3 +++
>  include/uapi/linux/kernel-page-flags.h | 1 +
>  3 files changed, 10 insertions(+)
>
> diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
> index c9266340852c..5896b7d7fd74 100644
> --- a/Documentation/vm/pagemap.txt
> +++ b/Documentation/vm/pagemap.txt
> @@ -64,6 +64,7 @@ There are five components to pagemap:
>      22. THP
>      23. BALLOON
>      24. ZERO_PAGE
> +    25. IDLE
>
>   * /proc/kpagecgroup.  This file contains a 64-bit inode number of the
>     memory cgroup each page is charged to, indexed by PFN. Only available when
> @@ -124,6 +125,11 @@ Short descriptions to the page flags:
>  24. ZERO_PAGE
>      zero page for pfn_zero or huge_zero page
>
> +25. IDLE
> +    page has not been accessed since it was marked idle (see /proc/kpageidle)
> +    Note that this flag may be stale in case the page was accessed via a PTE.
> +    To make sure the flag is up-to-date one has to read /proc/kpageidle first.
> +
>      [IO related page flags]
>   1. ERROR     IO error occurred
>   3. UPTODATE  page has up-to-date data
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 273537885ab4..13dcb823fe4e 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -150,6 +150,9 @@ u64 stable_page_flags(struct page *page)
>         if (PageBalloon(page))
>                 u |= 1 << KPF_BALLOON;
>
> +       if (page_is_idle(page))
> +               u |= 1 << KPF_IDLE;
> +
>         u |= kpf_copy_bit(k, KPF_LOCKED,        PG_locked);
>
>         u |= kpf_copy_bit(k, KPF_SLAB,          PG_slab);
> diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
> index a6c4962e5d46..5da5f8751ce7 100644
> --- a/include/uapi/linux/kernel-page-flags.h
> +++ b/include/uapi/linux/kernel-page-flags.h
> @@ -33,6 +33,7 @@
>  #define KPF_THP                        22
>  #define KPF_BALLOON            23
>  #define KPF_ZERO_PAGE          24
> +#define KPF_IDLE               25
>
>
>  #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
> --
> 2.1.4
>



-- 
Andres Lagar-Cavilla | Google Kernel Team | andreslc@...gle.com
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