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From: "Theodore Ts'o" <tytso@mit.edu>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>,
	Zhang Yi <yi.zhang@huawei.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	adilger.kernel@dilger.ca, yukuai3@huawei.com
Subject: Re: [RFC PATCH v2 7/7] ext4: fix race between blkdev_releasepage() and ext4_put_super()
Date: Fri, 23 Apr 2021 10:40:38 -0400	[thread overview]
Message-ID: <YILcZpQh8T//6HLb@mit.edu> (raw)
In-Reply-To: <20210422090410.GA26221@quack2.suse.cz>

On Thu, Apr 22, 2021 at 11:04:11AM +0200, Jan Kara wrote:
> Yes, I understand that. What I was more asking about is: Does it really
> matter we leave those buffer heads and journal heads unreclaimed. I
> understand it could be triggering premature OOM in theory but is it a
> problem in practice? Was there some observed practical case for which this
> was added or was it just added due to the theoretical concern?

I was doing some research, and found the mail thread which inspired
bdev_try_to_free_page():

https://lore.kernel.org/linux-ext4/20081202200647.72cc5807.toshi.okajima@jp.fujitsu.com/

From what I can tell Toshi Okajima did have a test workload which
would trigger blkdev_releasepage().  He didn't specify it in the mail
thread as near as I can tell, but he did use it to test the page.
Thinking about it, it shouldn't be hard to trigger it via something like:

   find /mnt -print0 | xargs -0 touch

in a memory contrained box with a large file system attached (a
bookshelf NAS scenario).  Under the right circumstances, I'm pretty
sure a premature OOM could be demonstrated.

					- Ted

      parent reply	other threads:[~2021-04-23 14:41 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-14 13:47 [RFC PATCH v2 0/7] ext4, jbd2: fix 3 issues about bdev_try_to_free_page() Zhang Yi
2021-04-14 13:47 ` [RFC PATCH v2 1/7] jbd2: remove the out label in __jbd2_journal_remove_checkpoint() Zhang Yi
2021-04-21 10:01   ` Jan Kara
2021-04-14 13:47 ` [RFC PATCH v2 2/7] jbd2: ensure abort the journal if detect IO error when writing original buffer back Zhang Yi
2021-04-21 13:20   ` Jan Kara
2021-04-14 13:47 ` [RFC PATCH v2 3/7] jbd2: don't abort the journal when freeing buffers Zhang Yi
2021-04-21 13:23   ` Jan Kara
2021-04-14 13:47 ` [RFC PATCH v2 4/7] jbd2: do not free buffers in jbd2_journal_try_to_free_buffers() Zhang Yi
2021-04-15 14:46   ` Christoph Hellwig
2021-04-14 13:47 ` [RFC PATCH v2 5/7] ext4: use RCU to protect accessing superblock in blkdev_releasepage() Zhang Yi
2021-04-15 14:48   ` Christoph Hellwig
2021-04-14 13:47 ` [RFC PATCH v2 6/7] fs: introduce a usage count into the superblock Zhang Yi
2021-04-15 14:40   ` Christoph Hellwig
2021-04-16  8:00     ` Zhang Yi
2021-04-14 13:47 ` [RFC PATCH v2 7/7] ext4: fix race between blkdev_releasepage() and ext4_put_super() Zhang Yi
2021-04-15 14:52   ` Christoph Hellwig
2021-04-16  8:00     ` Zhang Yi
2021-04-20 13:08       ` Christoph Hellwig
2021-04-21 13:46         ` Jan Kara
2021-04-21 16:57           ` Theodore Ts'o
2021-04-22  9:04             ` Jan Kara
2021-04-23 11:39               ` Zhang Yi
2021-04-23 16:06                 ` Jan Kara
2021-04-23 14:40               ` Theodore Ts'o [this message]

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