On Sun, 16 September 2007 11:15:36 -0700, Linus Torvalds wrote:
> On Sun, 16 Sep 2007, Jörn Engel wrote:
> >
> > I have been toying with the idea of having seperate caches for pinned
> > and movable dentries. Downside of such a patch would be the number of
> > memcpy() operations when moving dentries from one cache to the other.
>
> Totally inappropriate.
>
> I bet 99% of all "dentry_lookup()" calls involve turning the last dentry
> from having a count of zero ("movable") to having a count of 1 ("pinned").
>
> So such an approach would fundamentally be broken. It would slow down all
> normal dentry lookups, since the *common* case for leaf dentries is that
> they have a zero count.
Why am I not surprised? :)
> So it's much better to do it on a "directory/file" basis, on the
> assumption that files are *mostly* movable (or just freeable). The fact
> that they aren't always (ie while kept open etc), is likely statistically
> not all that important.
My approach is to have one for mount points and ramfs/tmpfs/sysfs/etc.
which are pinned for their entire lifetime and another for regular
files/inodes. One could take a three-way approach and have
always-pinned, often-pinned and rarely-pinned.
We won't get never-pinned that way.
Jörn
--
The wise man seeks everything in himself; the ignorant man tries to get
everything from somebody else.
-- unknown
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