From: Al Viro <viro@zeniv.linux.org.uk>
To: Waiman Long <longman@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Christian Brauner <brauner@kernel.org>
Subject: Re: [PATCH v2] vfs: Pre-allocate superblock in sget_fc() if !test
Date: Mon, 31 Jan 2022 03:11:59 +0000 [thread overview]
Message-ID: <YfdTfxtUIpKp0mUR@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <20220124161006.141323-1-longman@redhat.com>
On Mon, Jan 24, 2022 at 11:10:06AM -0500, Waiman Long wrote:
> When the test function is not defined in sget_fc(), we always need
> to allocate a new superblock. So there is no point in acquiring the
> sb_lock twice in this case. Optimize the !test case by pre-allocating
> the superblock first before acquring the lock.
Umm... Do you really see the contention on that sucker? Because if you
do, I'd expect sget_fc() to be the least of your problems.
TBH, I'd be very surprised if that had caused measurable improvement in
any setup. Seriously, take a look at alloc_super(). If spin_lock() +
spin_unlock() + branch is noticable among all that... And it's not
as if you were not going to dirty that cacheline shortly afterwards
anyway, so cacheline pingpong is not an issue either...
I'm not saying that the patch is broken, I'm just wondering if it's worth
bothering with.
prev parent reply other threads:[~2022-01-31 3:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-24 16:10 [PATCH v2] vfs: Pre-allocate superblock in sget_fc() if !test Waiman Long
2022-01-25 13:29 ` Christian Brauner
2022-01-31 3:11 ` Al Viro [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YfdTfxtUIpKp0mUR@zeniv-ca.linux.org.uk \
--to=viro@zeniv.linux.org.uk \
--cc=brauner@kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox