Re: Upcoming: Notifications, FS notifications and fsinfo()

[Miklos Szeredi]

On Wed, Apr 1, 2020 at 6:07 PM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>
> > I've still not heard a convincing argument in favor of a syscall.
>
> From your own results, scanning 10000 mounts through mountfs and reading just
> two values from each is an order of magnitude slower without the effect of the
> dentry/inode caches.  It gets faster on the second run because the mountfs
> dentries and inodes are cached - but at a cost of >205MiB of RAM.  And it's
> *still* slower than fsinfo().

Already told you that we can just delete the dentry on dput_final, so
the memory argument is immaterial.

And the speed argument also, because there's no use case where that
would make a difference.  You keep bringing up the notification queue
overrun when watching a subtree, but that's going to be painful with
fsinfo(2) as well.   If that's a relevant use case (not saying it's
true), might as well add a /mnt/MNT_ID/subtree_info (trivial again)
that contains all information for the subtree.  Have fun implementing
that with fsinfo(2).

Thanks,
Miklos