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

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Message-ID: <20180424061700.GA3689@avx2>
Date:   Tue, 24 Apr 2018 09:17:00 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     jeffm@...e.com
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC] [PATCH 0/5] procfs: reduce duplication by using symlinks

On Mon, Apr 23, 2018 at 10:21:01PM -0400, jeffm@...e.com 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.