From: Andrew Morton <akpm@linux-foundation.org>
To: Fengguang Wu <fengguang.wu@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Rik van Riel <riel@redhat.com>, Theodore Ts'o <tytso@mit.edu>,
"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH] resolve duplicate flag no for PG_lazyfree
Date: Sun, 13 May 2007 22:46:30 -0700 [thread overview]
Message-ID: <20070513224630.3cd0cb54.akpm@linux-foundation.org> (raw)
In-Reply-To: <379110250.28666@ustc.edu.cn>
On Mon, 14 May 2007 10:37:18 +0800 Fengguang Wu <fengguang.wu@gmail.com> wrote:
> PG_lazyfree and PG_booked shares the same bit.
>
> Either it is a bug that shall fixed by the following patch, or
> the situation should be explicitly documented?
>
> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
> ---
> include/linux/page-flags.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- linux-2.6.21-mm2.orig/include/linux/page-flags.h
> +++ linux-2.6.21-mm2/include/linux/page-flags.h
> @@ -91,7 +91,7 @@
> #define PG_buddy 19 /* Page is free, on buddy lists */
> #define PG_booked 20 /* Has blocks reserved on-disk */
>
> -#define PG_lazyfree 20 /* MADV_FREE potential throwaway */
> +#define PG_lazyfree 21 /* MADV_FREE potential throwaway */
>
> /* PG_owner_priv_1 users should have descriptive aliases */
> #define PG_checked PG_owner_priv_1 /* Used by some filesystems */
That's an accident: PG_lazyfree got added but the out-of-tree ext4 patches
didn't get updated.
otoh, the intersection between pages which are PageBooked() and pages which
are PageLazyFree() should be zreo, so it'd be good to actually formalise
this reuse within the ext4 patches.
otoh2, PageLazyFree() could have reused PG_owner_priv_1.
Rik, Ted: any thoughts? We do need to scrimp on page flags: when we
finally run out, we're screwed.
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next parent reply other threads:[~2007-05-14 5:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <379110250.28666@ustc.edu.cn>
2007-05-14 5:46 ` Andrew Morton [this message]
[not found] ` <20070514075519.GA6255@mail.ustc.edu.cn>
2007-05-14 7:55 ` [PATCH] resolve duplicate flag no for PG_lazyfree Fengguang Wu
2007-05-14 7:55 ` Fengguang Wu
2007-05-14 18:06 ` Theodore Tso
2007-05-14 20:46 ` Andrew Morton
2007-05-16 0:28 ` Nick Piggin
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