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From: Jeff Mahoney <jeffm@suse.com>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Al Viro <viro@zeniv.linux.org.uk>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Oleg Nesterov <oleg@redhat.com>
Subject: Re: [RFC] [PATCH 0/5] procfs: reduce duplication by using symlinks
Date: Wed, 25 Apr 2018 14:04:30 -0400	[thread overview]
Message-ID: <43fd713e-1ebf-7250-5ddb-e0326e0c3376@suse.com> (raw)
In-Reply-To: <20180424061700.GA3689@avx2>

On 4/24/18 2:17 AM, Alexey Dobriyan wrote:
> On Mon, Apr 23, 2018 at 10:21:01PM -0400, jeffm@suse.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),

It's a pretty common pattern in the kernel, but it's just as easy to set
inode->i_link during instantiation and keep RCU lookup.  There aren't so
many of these to make it a real burden on memory.

> * "%.*s" for dentry names is probably unnecessary,
>   they're always NUL terminated

Ack.

> * kasprintf() does printing twice, since we're kind of care about /proc
>   performance, allocate for the worst case.

Ack, integrated with ->get_link fix.

> * "int nlinks = nlink_tgid;"
>   Unsigned police.

Ack.  nlink_t{,g}id are both u8, but it's easy to make it consistent.

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

Ack.

Notes of my own:

proc_task_count_links also had the logic backward.  It would add an
extra link to the count for the symlink rather than the dir.

proc_pid_files_revalidate only needs to check if the tasks share files
since it won't be called if it's not a symlink.

Thanks for the review,

-Jeff

-- 
Jeff Mahoney
SUSE Labs

  reply	other threads:[~2018-04-25 18:04 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-24  2:21 jeffm
2018-04-24  2:21 ` [PATCH 1/5] procfs: factor out a few helpers jeffm
2018-04-24  2:21 ` [PATCH 2/5] procfs: factor out inode revalidation work from pid_revalidation jeffm
2018-04-24  2:21 ` [PATCH 3/5] procfs: use symlinks for /proc/<pid>/task when not thread group leader jeffm
2018-04-24  2:21 ` [PATCH 4/5] procfs: share common directories between /proc/tgid and /proc/tgid/task/tgid jeffm
2018-04-24  2:21 ` [PATCH 5/5] procfs: share fd/fdinfo with thread group leader when files are shared jeffm
2018-04-24 15:41   ` kbuild test robot
2018-04-24 15:41   ` [RFC PATCH] procfs: proc_pid_files_link_dentry_operations can be static kbuild test robot
2018-04-24  6:17 ` [RFC] [PATCH 0/5] procfs: reduce duplication by using symlinks Alexey Dobriyan
2018-04-25 18:04   ` Jeff Mahoney [this message]
2018-04-24 14:14 ` Eric W. Biederman
2018-04-26 21:03   ` Jeff Mahoney
2019-03-21 18:30   ` Jeff Mahoney
2019-03-23 15:56     ` Eric W. Biederman
2019-03-24  3:01       ` Jeff Mahoney

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