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.
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.
Linus
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