From: Theodore Ts'o <tytso@mit.edu>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Gioh Kim <gioh.kim@lge.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Andreas Dilger <adilger.kernel@dilger.ca>,
linux-ext4@vger.kernel.org
Subject: Re: [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable area
Date: Tue, 22 Jul 2014 04:14:40 -0400 [thread overview]
Message-ID: <20140722081440.GA5137@thunk.org> (raw)
In-Reply-To: <20140722073005.GT3935@laptop>
On Tue, Jul 22, 2014 at 09:30:05AM +0200, Peter Zijlstra wrote:
> > I introduce a new API for allocating page from non-movable area.
> > It is useful for ext4 and others that want to hold page cache for a long time.
>
> There's no word on why you can't teach ext4 to still migrate that page.
> For all I know it might be impossible, but at least mention why.
In theory we might be able to do it, but it's only a single 4k page,
and we'd have to add RCU locking all over the place in order to be
able to switch out the superblock structure, since we reference it all
over the place inside fs/ext4. The question I'd ask is is it worth
it.
I suspect the bigger deal is that there are all sorts of inodes and
dentries which are effectively pinned and thus, impossible to migrate.
This probably locks down many more pages (by a fact of at least 10 or
20), and I'd think that's something you would be much more interested
in fixing.
- Ted
next prev parent reply other threads:[~2014-07-22 8:14 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-22 5:18 [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable area Gioh Kim
2014-07-22 7:30 ` Peter Zijlstra
2014-07-22 8:14 ` Theodore Ts'o [this message]
2014-07-27 1:01 ` Theodore Ts'o
2014-07-30 7:56 ` Gioh Kim
2014-07-22 9:38 ` Jan Kara
2014-07-30 7:44 ` Gioh Kim
2014-07-30 7:57 ` Kyungmin Park
2014-07-30 10:11 ` Jan Kara
2014-07-30 10:19 ` Peter Zijlstra
2014-07-30 23:45 ` Gioh Kim
2014-07-30 23:54 ` Gioh Kim
2014-07-31 0:03 ` Jan Kara
2014-07-31 0:37 ` Gioh Kim
2014-07-31 12:21 ` Jan Kara
2014-08-01 0:07 ` Gioh Kim
2014-08-01 1:06 ` Gioh Kim
2014-08-01 9:57 ` Jan Kara
2014-08-01 13:36 ` Peter Zijlstra
2014-08-01 15:24 ` Jan Kara
2014-08-01 16:04 ` Peter Zijlstra
2014-08-06 6:15 ` Gioh Kim
2014-08-01 8:34 ` Joonsoo Kim
2014-08-01 9:15 ` Jan Kara
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=20140722081440.GA5137@thunk.org \
--to=tytso@mit.edu \
--cc=adilger.kernel@dilger.ca \
--cc=akpm@linux-foundation.org \
--cc=gioh.kim@lge.com \
--cc=jack@suse.cz \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=viro@zeniv.linux.org.uk \
/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;
as well as URLs for NNTP newsgroup(s).