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
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next prev parent reply other threads:[~2014-09-17 1:25 UTC|newest]
Thread overview: 11+ 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 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 13:56 ` Peter Zijlstra
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