On 07/14/2018 02:34 PM, Al Viro wrote: > On Sat, Jul 14, 2018 at 11:00:32AM -0700, Linus Torvalds wrote: >> On Sat, Jul 14, 2018 at 10:35 AM Pavel Machek <pa...@ucw.cz> 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 > any.
Normally you need to be root or have privileges to mount a filesystem. Right? I am aware there is effort going on to allow non-privilege user mount in container. That can open a can of worms if it is not done properly. With privileges, there is a lot of ways one can screw up the system. So I am not less concern about this particular issue. Cheers, Longman
