On Sat, Jul 14, 2018 at 11:00:32AM -0700, Linus Torvalds wrote: > On Sat, Jul 14, 2018 at 10:35 AM Pavel Machek <pavel@xxxxxx> 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.
