Re: Use of READDIRPLUS on large directories

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Mar 17, 2011 at 11:55:22AM +1100, NeilBrown wrote:
> Strangely, when I try NFSv4 I don't get what I would expect.
> 
> "ls" on an unpatched 2.6.38 takes over 5 seconds rather than around 4.
> With the patch it does back down to about 2. (still NFSv3 at 1.5).
> Why would NFSv4 be slower?
>  On v3 we make 44 READDIRPLUS calls and 284 READDIR calls - total of  328
>        READDIRPLUS have about 30 names, READDIR have about 100
>  On v4 we make 633 READDIR calls - nearly double.
>        Early packed contain about 19 name, later ones about 70
> 
> Is nfsd (2.6.32) just not packing enough answers in the reply?
> Client asks for a dircount of 16384 and a maxcount of 32768, and gets
> packets which are about 4K long - I guess that is PAGE_SIZE ??

>From nfsd4_encode_readdir():

	maxcount = PAGE_SIZE;
	if (maxcount > readdir->rd_maxcount)
		maxcount = readdir->rd_maxcount;

Unfortunately, I don't think the xdr encoding is equipped to deal with
page boundaries.  It should be.

--b.