From: Jan Kara <jack@suse.cz>
To: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Cc: Theodore Ts'o <tytso@mit.edu>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH -v3] vfs: add releasepages hooks to block devices which can be used by file systems
Date: Thu, 18 Dec 2008 14:12:34 +0100 [thread overview]
Message-ID: <20081218131222.GB13580@duck.suse.cz> (raw)
In-Reply-To: <4949DC6D.3050908@jp.fujitsu.com>
Hello,
On Thu 18-12-08 14:15:25, Toshiyuki Okajima wrote:
> > > > From: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
> > > >
> > > > Implement blkdev_releasepage() to release the buffer_heads and page
> > > > after we release private data which belongs to a client of the block
> > > > device, such as a filesystem.
> > > >
> > > > blkdev_releasepage() call the client's releasepage() which is
> > > > registered by blkdev_register_client_releasepage() to release its
> > > > private data.
> > Yes, this is IMO the right fix. I'm just wondering about the fact that we
> > can't block in the client_releasepage(). That seems to be caused by the fact
> > that we need to be protected against client_releasepage() callback changes
> > which essentially means umount, right? I'm not saying I have a better solution
> > but introducing such limitation seems stupid just because of umount...
> >
> Difference between v2 and v3 in blkdev_releasepage:
> < ret = (*ei->client_releasepage)(ei->client, page, wait);
> < else
> --
> > /*
> > * Since we are holding a spinlock (ei->client_lock),
> > * make sure the client_releasepage function
> > * understands that it must not block.
> > */
> > ret = (*ei->client_releasepage)(ei->client, page,
> > wait & ~__GFP_WAIT);
> > else
>
> Ask for clarification.
Yes, my question was more about the original design of the patch than
about the particular fix. Sorry for the confusion.
> Which of the following do you mean:
> 1) If using a spinlock in client_releasepage() is only for mount/umount,
> this implementation is not wise.
> 2) There is the fact that a spinlock is necessary for blkdev_releasepage().
> This fact prevents us from making various implementations of
> client_releasepage().
> (Without a spinlock, we can implement a client_releasepage() which can release
> the buffers with a sleep. As a result, it may enable more buffers release than
> before.)
>
> There is the fact that a filesystem can be mounted on several places,
> and the lock mechanism is absolutely necessary for this fact.
This is the thing I was wondering about. Why exactly is the spinlock
necessary for blkdev_releasepage()? I understand we have to protect
reading client_releasepage() pointer because it could change but my point
was that it changes only during mount / umount.
> I also think we are sad that we cannot implement various implementations for
> client_releasepage(). But now I cannot imagine what to do for
> a client_releasepage() which can sleep, too...
Regards
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2008-12-18 13:12 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-02 11:06 [BUG][PATCH 1/4] ext3: fix a cause of __schedule_bug via blkdev_releasepage Toshiyuki Okajima
2008-12-08 14:01 ` Theodore Tso
2008-12-08 14:06 ` [PATCH -V2] ext3: provide function to release metadata pages under memory pressure Theodore Ts'o
2008-12-08 14:06 ` [PATCH -V2] ext4: " Theodore Ts'o
2008-12-12 0:54 ` [BUG][PATCH 1/4] ext3: fix a cause of __schedule_bug via blkdev_releasepage Toshiyuki Okajima
2008-12-12 6:21 ` Theodore Tso
2008-12-12 17:52 ` [PATCH -v3] vfs: add releasepages hooks to block devices which can be used by file systems Theodore Ts'o
2008-12-12 17:52 ` [PATCH -v3] ext3: provide function to release metadata pages under memory pressure Theodore Ts'o
2008-12-12 17:52 ` [PATCH -v3] ext4: " Theodore Ts'o
2008-12-17 15:39 ` [PATCH -v3] vfs: add releasepages hooks to block devices which can be used by file systems Jan Kara
2008-12-18 5:15 ` Toshiyuki Okajima
2008-12-18 13:12 ` Jan Kara [this message]
2008-12-18 14:54 ` Theodore Tso
2008-12-18 16:38 ` Jan Kara
2008-12-19 5:15 ` Toshiyuki Okajima
2008-12-26 5:01 ` Al Viro
2009-01-03 15:09 ` Theodore Ts'o
2009-01-03 15:09 ` [PATCH 1/3] add releasepage " Theodore Ts'o
2009-01-03 15:09 ` [PATCH 2/3] ext3: provide function to release metadata pages under memory pressure Theodore Ts'o
2009-01-03 15:09 ` [PATCH 3/3] ext4: " Theodore Ts'o
2009-01-05 8:16 ` [PATCH 1/3] add releasepage hooks to block devices which can be used by file systems Toshiyuki Okajima
2009-01-05 16:05 ` Theodore Tso
2009-01-06 4:07 ` Toshiyuki Okajima
2009-01-06 4:29 ` Theodore Tso
2008-12-15 2:21 ` [BUG][PATCH 1/4] ext3: fix a cause of __schedule_bug via blkdev_releasepage Toshiyuki Okajima
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