Re: [PATCH] NFS: filelayout should use nfs_generic_pg_test

[Boaz Harrosh <bharrosh@panasas.com>]

On 06/01/2011 10:17 PM, Trond Myklebust wrote:
> On Wed, 2011-06-01 at 21:56 +0300, Benny Halevy wrote:
> 
>> For pnfs, we need to ignore wsize, meaning we first need to try
>> to coalesce the pages and then decide if we're going the nfs_flush_multi
>> or the nfs_flush_one way, based on the coalesced length.
> 
> No! Ignoring the wsize is definitely wrong... If the stripe size is
> larger than the 'maxwrite' recommended attribute, then the DS is allowed
> to do a short write, in which case we have to resend.
> 

As far as I could understand the current code, desc->bsize which derives
from wsize/rsize is negotiated with the MDS. But the wsize in question
is the DS's one. So I think in pnfs it is only the layout-driver that
can check this properly against the filer in question. Only if IO is
to go through MDS the bsize check is relevant.

BTW: The BUG_ON() Andy hit, does not look like an hard bug to fix ;-)

> In any case, nfs_flush_multi and nfs_flush_one need a rewrite in order
> to deal properly with O_DIRECT writes, and so I'm expecting to get rid
> of the single nfs_page limit for the r/wsize<PAGE_SIZE case.
> Please don't make any large changes to this code at this time.
> 

Amen, Good riddance
Boaz