From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Wed, 5 Jul 2000 14:35:19 +0100
From: "Stephen C. Tweedie" <sct@redhat.com>
Subject: Re: User mode stalls - can it be...?
Message-ID: <20000705143519.D1290@redhat.com>
References: <3962874A.190AAC7E@norran.net> <39628F72.4987A36@norran.net>
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In-Reply-To: <39628F72.4987A36@norran.net>; from roger.larsson@norran.net on Wed, Jul 05, 2000 at 03:29:22AM +0200
Sender: owner-linux-mm@kvack.org
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To: Roger Larsson <roger.larsson@norran.net>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>
List-ID: <linux-mm.kvack.org>

Hi,

On Wed, Jul 05, 2000 at 03:29:22AM +0200, Roger Larsson wrote:
> 
> static void sync_page_buffers(struct buffer_head *bh, int wait)
> {
> 	struct buffer_head * tmp = bh;
> 
> 	do {
> 		struct buffer_head *p = tmp;
> 		tmp = tmp->b_this_page;
> 		if (!buffer_locked(p) &&
>                     buffer_dirty(p))
> 			ll_rw_block(WRITE, 1, &p);
> 		if (wait)
> 			__wait_on_buffer(p);
> 	} while (tmp != bh);

Yikes no.  That will make the syncer wait for every single write
synchronously.  It will cause a page full of 1k buffers to be written
out as four separate 1k writes instead of being streamed.  This will
_kill_ performance.

Cheers,
 Stephen
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