Re: Why NFS enforce size limit on readdirplus

[Trond Myklebust]

On Fri, 2006-06-02 at 01:54 -0400, Xin Zhao wrote:
> Maybe this question is a little dumb.
> 
> I am wondering why in NFS readdirplus can be used only for directories
> of size less than 8*PAGE_SIZE, otherwise, it will switch to use normal
> readdir?
> 
> In nfs/inode.c, I noticed the following code:
> 			    if (nfs_server_capable(inode, NFS_CAP_READDIRPLUS) &&
> fattr->size <= NFS_LIMIT_READDIRPLUS)
> 				    set_bit(NFS_INO_ADVISE_RDPLUS, &NFS_FLAGS(inode));
> 
> Can someone kindly explain the reason?

Efficiency: READDIRPLUS requires a lookup for each entry. If there are
too many entries, the whole thing gets really really slow...

Cheers,
  Trond

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