linux-kernel - Re: NILFS2 get stuck after bio

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Date:	Sun, 14 Jun 2009 10:00:06 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
Cc:	albertito@...tiri.com.ar, llucax@...il.com,
	linux-kernel@...r.kernel.org, users@...fs.org
Subject: Re: NILFS2 get stuck after bio_alloc() fail

On Sun, Jun 14, 2009 at 9:30 AM, Ryusuke
Konishi<konishi.ryusuke@....ntt.co.jp> wrote:
> The original GFP flag was GFP_NOIO, but replaced to GFP_NOWAIT at a
> preliminary release in February 2008.  It was because a user
> experienced system memory shortage by the bio_alloc() call.
>
> Even though nilfs_alloc_seg_bio() repeatedly calls bio_alloc()
> reducing the number of bio vectors in case of failure, this fallback
> did not work well.
>
> I'm in two minds whether I should change it back to GFP_NOIO.
> Or should I switch the gfp as follows?

As far as I can tell, the only difference with GFP_NOIO and GFP_NOWAIT
here is that the former will trigger the mempool_alloc() page reclaim
path. But I am not sure I understand why switching to GFP_NOWAIT
helped with memory shortage. What exactly was the problem there?

                                 Pekka
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