From: Theodore Ts'o <tytso@mit.edu>
To: Hugh Dickins <hughd@google.com>
Cc: Andreas Dilger <adilger@dilger.ca>,
Christoph Lameter <cl@linux.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-mm <linux-mm@kvack.org>,
linux-ext4@vger.kernel.org
Subject: Re: Best way to pin a page in ext4?
Date: Tue, 16 Sep 2014 21:25:42 -0400 [thread overview]
Message-ID: <20140917012542.GO6205@thunk.org> (raw)
In-Reply-To: <alpine.LSU.2.11.1409161555120.5144@eggly.anvils>
On Tue, Sep 16, 2014 at 05:07:18PM -0700, Hugh Dickins wrote:
> You might (I'm not certain) be able to get away with extending the
> use of mlock_vma_page() and munlock_vma_page() in this (admittedly
> attractive) way, up until someone mmap's that range (and mlocks
> then munlocks it? again, I'm not certain if that's necessary).
> Then the PageMlocked flag is liable to be cleared, because the
> page will not be found in any mlock'ed vma; and the page can
> then be reclaimed behind your back (statistics gone wrong too?
> again I'm not sure).
>
> Now, I expect it's unlikely (impossible?) for anyone to mmap your
> bitmap pages while they're being used as filesystem metadata (rather
> than mere blockdev pages). But you can see why we would prefer not
> to export those functions.
Yes, it's impossible for anyone to mmap the pages from
EXT4_SB(sb)->s_buddy_cache inode, because it's not exposed in any way
to userspace. But I can see why you wouldn't want it to be used
almost anywhere else.
> For now I agree with Andreas, just grab an extra refcount; but you're
> right that leaving these pages on evictable LRUs is regrettable,
> and can be inefficient under reclaim.
OK, fair enough, that seems simpler all around.
Cheers,
- Ted
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2014-09-17 1:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-15 18:51 Best way to pin a page in ext4? Theodore Ts'o
2014-09-15 20:57 ` Andreas Dilger
2014-09-16 18:07 ` Theodore Ts'o
2014-09-16 18:34 ` Christoph Lameter
2014-09-16 18:56 ` Theodore Ts'o
2014-09-17 0:07 ` Hugh Dickins
2014-09-17 0:07 ` Hugh Dickins
2014-09-17 1:25 ` Theodore Ts'o [this message]
2014-09-17 3:31 ` Christoph Lameter
2014-09-17 13:57 ` Peter Zijlstra
2014-09-17 20:37 ` Hugh Dickins
2014-09-17 20:37 ` Hugh Dickins
2014-09-17 13:56 ` Peter Zijlstra
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=20140917012542.GO6205@thunk.org \
--to=tytso@mit.edu \
--cc=adilger@dilger.ca \
--cc=cl@linux.com \
--cc=hughd@google.com \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=peterz@infradead.org \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.