[lkml]   [2018]   [Jul]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v5 0/6] fs/dcache: Track & limit # of negative dentries
On Sat, Jul 14, 2018 at 11:00:32AM -0700, Linus Torvalds wrote:
> On Sat, Jul 14, 2018 at 10:35 AM Pavel Machek <> wrote:
> >
> > Could we allocate -ve entries from separate slab?
> No, because negative dentrires don't stay negative.
> Every single positive dentry starts out as a negative dentry that is
> passed in to "lookup()" to maybe be made positive.
> And most of the time they <i>do</i> turn positive, because most of the
> time people actually open files that exist.
> But then occasionally you don't, because you're just blindly opening a
> filename whether it exists or not (to _check_ whether it's there).

BTW, one point that might not be realized by everyone: negative dentries
are *not* the hard case.
mount -t tmpfs none /mnt
touch /mnt/a
for i in `seq 100000`; do ln /mnt/a /mnt/$i; done

and you've got 100000 *unevictable* dentries, with the time per iteration
being not all that high (especially if you just call link(2) in a loop).
They are all positive and all pinned. And you've got only one inode
there and no persistently opened files, so rlimit and quota won't help
 \ /
  Last update: 2018-07-15 22:07    [W:0.089 / U:0.412 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site