From: Chao Yu <chao@kernel.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Eric Biggers <ebiggers@kernel.org>,
Jaegeuk Kim <jaegeuk@kernel.org>,
linux-f2fs-devel@lists.sourceforge.net,
linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
Satya Tangirala <satyaprateek2357@gmail.com>,
Changheun Lee <nanich.lee@samsung.com>,
Matthew Bobrowski <mbobrowski@mbobrowski.org>
Subject: Re: [PATCH 3/9] f2fs: rework write preallocations
Date: Thu, 29 Jul 2021 08:26:18 +0800 [thread overview]
Message-ID: <e237ab66-82dd-254d-7be2-aee8cb2b1c85@kernel.org> (raw)
In-Reply-To: <20210727153335.GE559212@magnolia>
On 2021/7/27 23:33, Darrick J. Wong wrote:
> On Tue, Jul 27, 2021 at 04:30:16PM +0800, Chao Yu wrote:
>> On 2021/7/27 15:38, Eric Biggers wrote:
>>> That's somewhat helpful, but I've been doing some more investigation and now I'm
>>> even more confused. How can f2fs support non-overwrite DIO writes at all
>>> (meaning DIO writes in LFS mode as well as DIO writes to holes in non-LFS mode),
>>> given that it has no support for unwritten extents? AFAICS, as-is users can
>>
>> I'm trying to pick up DAX support patch created by Qiuyang from huawei, and it
>> looks it faces the same issue, so it tries to fix this by calling sb_issue_zeroout()
>> in f2fs_map_blocks() before it returns.
>
> I really hope you don't, because zeroing the region before memcpy'ing it
> is absurd. I don't know if f2fs can do that (xfs can't really) without
> pinning resources during a potentially lengthy memcpy operation, but you
> /could/ allocate the space in ->iomap_begin, attach some record of that
> to iomap->private, and only commit the mapping update in ->iomap_end.
Thanks for the suggestion, let me check this a little bit later, since now I
just try to stabilize the codes...
Thanks,
>
> --D
>
>>> easily leak uninitialized disk contents on f2fs by issuing a DIO write that
>>> won't complete fully (or might not complete fully), then reading back the blocks
>>> that got allocated but not written to.
>>>
>>> I think that f2fs will have to take the ext2 approach of not allowing
>>> non-overwrite DIO writes at all...
>> Yes,
>>
>> Another option is to enhance f2fs metadata's scalability which needs to update layout
>> of dnode block or SSA block, after that we can record the status of unwritten data block
>> there... it's a big change though...
>>
>> Thanks,
>>
>>>
>>> - Eric
>>>
next prev parent reply other threads:[~2021-07-29 0:26 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-16 14:39 [PATCH 0/9] f2fs: use iomap for direct I/O Eric Biggers
2021-07-16 14:39 ` [PATCH 1/9] f2fs: make f2fs_write_failed() take struct inode Eric Biggers
2021-07-25 10:00 ` Chao Yu
2021-07-16 14:39 ` [PATCH 2/9] f2fs: remove allow_outplace_dio() Eric Biggers
2021-07-19 8:41 ` Christoph Hellwig
2021-07-16 14:39 ` [PATCH 3/9] f2fs: rework write preallocations Eric Biggers
2021-07-25 10:50 ` Chao Yu
2021-07-25 17:57 ` Eric Biggers
2021-07-27 2:00 ` Jaegeuk Kim
2021-07-27 3:23 ` Chao Yu
2021-07-27 7:38 ` Eric Biggers
2021-07-27 8:30 ` Chao Yu
2021-07-27 15:33 ` Darrick J. Wong
2021-07-29 0:26 ` Chao Yu [this message]
2021-07-28 2:29 ` Jaegeuk Kim
2021-07-25 15:35 ` Jaegeuk Kim
2021-07-25 15:47 ` Jaegeuk Kim
2021-07-25 18:01 ` Eric Biggers
2021-07-26 19:04 ` Jaegeuk Kim
2021-07-16 14:39 ` [PATCH 4/9] f2fs: reduce indentation in f2fs_file_write_iter() Eric Biggers
2021-07-16 14:39 ` [PATCH 5/9] f2fs: fix the f2fs_file_write_iter tracepoint Eric Biggers
2021-07-16 14:39 ` [PATCH 6/9] f2fs: implement iomap operations Eric Biggers
2021-07-19 8:59 ` Christoph Hellwig
2021-07-22 20:47 ` Jaegeuk Kim
2021-07-22 20:49 ` Jaegeuk Kim
2021-07-22 20:54 ` Eric Biggers
2021-07-22 21:57 ` Jaegeuk Kim
2021-07-23 1:52 ` Eric Biggers
2021-07-23 5:00 ` Christoph Hellwig
2021-07-23 8:05 ` Eric Biggers
2021-07-16 14:39 ` [PATCH 7/9] f2fs: use iomap for direct I/O reads Eric Biggers
2021-07-16 14:39 ` [PATCH 8/9] f2fs: use iomap for direct I/O writes Eric Biggers
2021-07-16 14:39 ` [PATCH 9/9] f2fs: remove f2fs_direct_IO() Eric Biggers
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