Re: NILFS2 get stuck after bio_alloc() fail

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Sun, Jun 14, 2009 at 9:30 AM, Ryusuke
Konishi<konishi.ryusuke@lab.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