From: Jan Kara <jack@suse.cz>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org, yebin <yebin10@huawei.com>,
linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH RFC 2/2] block: Do not discard buffers under a mounted filesystem
Date: Tue, 25 Aug 2020 16:50:56 +0200 [thread overview]
Message-ID: <20200825145056.GC32298@quack2.suse.cz> (raw)
In-Reply-To: <20200825121616.GA10294@infradead.org>
On Tue 25-08-20 13:16:16, Christoph Hellwig wrote:
> On Tue, Aug 25, 2020 at 02:05:54PM +0200, Jan Kara wrote:
> > Discarding blocks and buffers under a mounted filesystem is hardly
> > anything admin wants to do. Usually it will confuse the filesystem and
> > sometimes the loss of buffer_head state (including b_private field) can
> > even cause crashes like:
>
> Doesn't work if the file system uses multiple devices.
Hum, right.
> I think we just really need to split the fs buffer_head address space
> from the block device one. Everything else is just going to cause a huge
> mess.
Do you mean that address_space filesystem uses to access its metadata on
/dev/sda will be different from the address_space you will see when reading
say /dev/sda? Thus these will be completely separate (and incoherent)
caches? Although this would be simple it will break userspace I'm afraid.
There are situations where tools read e.g. superblock of a mounted
filesystem from the block device and rely on the data to be reasonably
recent. Even worse e.g. tune2fs or e2fsck can *modify* superblock of a
mounted filesystem through the block device (e.g. to set 'fsck after X
mounts' fields and similar).
So we would need to somehow maintain at least vague coherence between these
caches which would be ugly.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-08-25 14:51 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 12:05 [PATCH RFC 0/2] Block and buffer invalidation under a filesystem Jan Kara
2020-08-25 12:05 ` [PATCH RFC 1/2] fs: Don't invalidate page buffers in block_write_full_page() Jan Kara
2020-08-25 12:05 ` [PATCH RFC 2/2] block: Do not discard buffers under a mounted filesystem Jan Kara
2020-08-25 12:16 ` Christoph Hellwig
2020-08-25 14:10 ` Theodore Y. Ts'o
2020-08-25 15:12 ` Jan Kara
2020-08-25 18:41 ` Matthew Wilcox
2020-08-25 18:49 ` Jan Kara
2020-08-25 14:50 ` Jan Kara [this message]
2020-08-27 7:16 ` Christoph Hellwig
2020-08-27 21:39 ` Al Viro
2020-08-28 0:07 ` Dave Chinner
2020-08-28 8:10 ` Jan Kara
2020-08-28 8:21 ` Andreas Dilger
2020-08-29 6:40 ` Christoph Hellwig
2020-08-31 7:48 ` Jan Kara
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