From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from norran.net (roger@t7o43p8.telia.com [194.237.168.128])
	by d1o43.telia.com (8.8.8/8.8.8) with ESMTP id DAA00949
	for <linux-mm@kvack.org>; Wed, 5 Jul 2000 03:32:59 +0200 (CEST)
Message-ID: <39628F72.4987A36@norran.net>
Date: Wed, 05 Jul 2000 03:29:22 +0200
From: Roger Larsson <roger.larsson@norran.net>
MIME-Version: 1.0
Subject: Re: User mode stalls - can it be...?
References: <3962874A.190AAC7E@norran.net>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: owner-linux-mm@kvack.org
Return-Path: <owner-linux-mm@kvack.org>
To: "linux-mm@kvack.org" <linux-mm@kvack.org>
List-ID: <linux-mm.kvack.org>

Roger Larsson wrote:

What about this modification (buffer.c):

 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)) {
			if (wait)
				__wait_on_buffer(p);
		} else if (buffer_dirty(p))
			ll_rw_block(WRITE, 1, &p);
	} while (tmp != bh);
}

-to-

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);
}


Not tested... (tomorrow - good night)

/RogerL

> 
> Hi,
> 
> I have an idea why we get the stalls!
> 
> If we end up in a situation where our write attempts are rejected
> due to lack of resources - we will continue happily with next and
> next...
> 
> Count hits zero and we return
> 
> But kswapd finds out that there is more to do and calls another
> shrink_mmap...
> (and need_resched is not set due to lower priority)
> 
> Gives, busy wait in shrink_mmap until pages are written...
> 
> I tried to renice 15 kswapd with improved results (I am using my patched
> kernels)
> Another approach would be to always sleep...
> 
> /RogerL
> 
> (Sent privately to Quintela and Riel - but it might be of value for
>  someone else too...)
> 
> --
> Home page:
>   http://www.norran.net/nra02596/
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux.eu.org/Linux-MM/

--
Home page:
  http://www.norran.net/nra02596/
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux.eu.org/Linux-MM/