linux-kernel - Re: [PATCH v2 4/4] fat: switch to fsinfo

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Message-ID: <873986h6qa.fsf@devron.myhome.or.jp>
Date:	Sat, 14 Apr 2012 20:51:09 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	dedekind1@...il.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Maling List <linux-kernel@...r.kernel.org>,
	Linux FS Maling List <linux-fsdevel@...r.kernel.org>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [PATCH v2 4/4] fat: switch to fsinfo_inode

Artem Bityutskiy <dedekind1@...il.com> writes:

>> > Sorry, I do not see how this can be true. You have a just bunch of dirty
>> > inodes, and it does not matter in which order you flush them. See
>> > __fat_write_inode() - it does not change the FAT table and does not
>> > affect the FSINFO block.
>> >
>> > Besides, the _current_ code first writes out FSINFO, because VFS calls
>> > ->sync_fs() first, then it starts writing back, then VFS calls
>> > ->sync_fs() for the second time.
>
> This is actually not exactly correct, but anyway, the first
> ->sync_fs(sb, 0) may come to FAT FS while it is in the middle of writing
> out the inodes.
>
> BTW, fat_clusters_flush() does not wait on the FSINFO block, which I
> think is a bug. I mean, it should call 'sync_dirty_buffer()'. I can
> submit a separate patch later.

write_super() is update and dirty buffer. Actual flush is via blockdev
(by historical reason), right? So, I think we don't need to wait at
sync_fs() in FATfs case.

>> Common case is delayed allocation though, in the case of FATfs, it would
>> be only truncate by last iput().
>
> Sorry, I do not understand what you mean. Do you still want me to take
> care of the order or not? If yes, could you please explain why?

Yes, I still worry about order. About ->sync_fs(), you are looking the
following?

__sync_filesystem(sb, 0)
__sync_filesystem(sb, 1)

Those are doing

1) try flush dirty all data at first without blocking
	__sync_filesystem(sb, 0)
2) wait some data of (1), and complete inodes work
	part of __sync_filesystem(sb, 1)
3) write super block to buffer
	->sync_fs() in __sync_filesystem(sb, 1)
4) flush and wait all metadata on blockdev
	__sync_blockdev() in __sync_filesystem(sb, 1)

right?

In your patch, we lose (3). (And I can't remember why I did it though,
your patch lose write_super() in ->put_super() too.)
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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