Re: [RFC] [PATCH 0/5] procfs: reduce duplication by using symlinks

From: Alexey Dobriyan
Date: Tue Apr 24 2018 - 02:17:09 EST

On Mon, Apr 23, 2018 at 10:21:01PM -0400, jeffm@xxxxxxxx wrote:
> Memory pressure isn't really an issue on this machine, so we
> end up using well over 100GB for proc files.

Text files at scale!

> With these patches applied, running the same testcase, the proc_inode
> cache only gets to about 600k objects, which is about 99.7% fewer. I
> get that procfs isn't supposed to be scalable, but this is kind of
> extreme. :)

Easy stuff:
* all ->get_link hooks are broken in RCU lookup (use GFP_KERNEL),
* "%.*s" for dentry names is probably unnecessary,
they're always NUL terminated
* kasprintf() does printing twice, since we're kind of care about /proc
performance, allocate for the worst case.

* "int nlinks = nlink_tgid;"
Unsigned police.

* (inode->i_mode & S_IFLNK)
this is sketchy, S_ISLNK exists.