Re: Eureka! (was Re: UTF-8 and case-insensitivity)

[viro]

On Thu, Feb 19, 2004 at 12:32:55PM -0800, Linus Torvalds wrote:
> Anyway, if we're willing to make some other changes to the VFS layer, we 
> could make all of this a bit more efficient by _not_ requiring the actual 
> filesystem lookup to take place.
> 
> If we had a flag that allowed a dentry to not have a d_inode pointer, but
> still _not_ be considered automatically negative, then we could just make
> a loop that fills the dcache directly from the readdir() data inside the
> kernel, without calling down to the filesystem to look up the inode.
> 
> That would save a _lot_ of memory - quite often we'd only need the dentry 
> itself.

> So then we could have a dcache that is fully populated, even though the
> actual inode data hasn't been loaded yet.
> 
> Comments?

*Ugh*

	That will cause all sorts of nastiness for filesystems that _have_
case-insensitive lookups.  Remember the crap we had to deal with to avoid
multiple dentries for directory?  It will come back, AFAICS.

	Another thing I really don't like is that we now get real lookups
on hashed dentry.  That potentially changes a lot and can lead to very
interesting results for some filesystems.
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