linux-kernel - Re: [PATCH 2/2] page-types.c: support KPF

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Message-Id: <20131007175016.a513865c5ecae4bd5759c2b0@linux-foundation.org>
Date:	Mon, 7 Oct 2013 17:50:16 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Wu Fengguang <fengguang.wu@...el.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] page-types.c: support KPF_SOFTDIRTY bit

On Fri,  4 Oct 2013 15:02:15 -0400 Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> Soft dirty bit allows us to track which pages are written since the
> last clear_ref (by "echo 4 > /proc/pid/clear_refs".) This is useful
> for userspace applications to know their memory footprints.
> 
> Note that the kernel exposes this flag via bit[55] of /proc/pid/pagemap,
> and the semantics is not a default one (scheduled to be the default in
> the near future.) However, it shifts to the new semantics at the first
> clear_ref, and the users of soft dirty bit always do it before utilizing
> the bit, so that's not a big deal. Users must avoid relying on the bit
> in page-types before the first clear_ref.

Is Documentation/filesystems/proc.txt (around line 450) fully up to
date here?

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