From: Andrea Arcangeli <andrea@suse.de>
To: Rajagopal Ananthanarayanan <ananth@sgi.com>
Cc: linux-kernel@vger.kernel.org, axboe@suse.de, torvalds@transmeta.com
Subject: Re: BH_Req question
Date: Tue, 10 Apr 2001 23:42:58 +0200 [thread overview]
Message-ID: <20010410234258.B6030@athlon.random> (raw)
In-Reply-To: <3AD36912.1F9E0654@sgi.com>
In-Reply-To: <3AD36912.1F9E0654@sgi.com>; from ananth@sgi.com on Tue, Apr 10, 2001 at 01:12:02PM -0700
On Tue, Apr 10, 2001 at 01:12:02PM -0700, Rajagopal Ananthanarayanan wrote:
>
> Hi,
>
> It seems BH_Req is set on a buffer_head by submit_bh.
> What part of the code unsets this flag during normal
> operations? One path seems to be block_flushpage->unmap_buffer
> ->clear_bit(BH_Req), but IIRC block_flushpage is used only
> for truncates. There must be another path to unset BH_Req
> under normal memory pressure, or (more unambiguously) on IO completion.
>
> So: in what ways can BH_Req be unset?
BH_Req is never unset until the buffer is destroyed (put back on the freelist).
BH_Req only says if such a buffer ever did any I/O yet or not. It is basically
only used to deal with I/O errors in sync_buffers().
> PS: In case why the question: I've got a system with tons of
> pages with buffers marked BH_Req, so try_to_free_buffers() bails
> out thinking that the buffer is busy ...
Either your debugging is wrong or you broke try_to_free_buffers because a
buffer with BH_Req must still be perfectly freeable.
Andrea
next prev parent reply other threads:[~2001-04-10 21:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-04-10 20:12 BH_Req question Rajagopal Ananthanarayanan
2001-04-10 21:42 ` Andrea Arcangeli [this message]
2001-04-10 22:03 ` Rajagopal Ananthanarayanan
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