From: Zhang Yi <yi.zhang@huaweicloud.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: "Darrick J. Wong" <djwong@kernel.org>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, brauner@kernel.org,
david@fromorbit.com, chandanbabu@kernel.org, tytso@mit.edu,
jack@suse.cz, yi.zhang@huawei.com, chengzhihao1@huawei.com,
yukuai3@huawei.com
Subject: Re: [PATCH v5 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks
Date: Fri, 26 Apr 2024 15:18:17 +0800 [thread overview]
Message-ID: <5b6228ce-c553-3387-dfc4-2db78e3bd810@huaweicloud.com> (raw)
In-Reply-To: <ZitKncYr0cCmU0NG@infradead.org>
On 2024/4/26 14:33, Christoph Hellwig wrote:
> On Fri, Apr 26, 2024 at 02:24:19PM +0800, Zhang Yi wrote:
>> Yeah, it looks more reasonable. But from the original scene, the
>> xfs_bmap_extsize_align() aligned the new extent that added to the cow fork
>> could overlaps the unreflinked range, IIUC, I guess that spare range is
>> useless exactly, is there any situation that would use it?
>
> I've just started staring at this (again) half an hour ago, and I fail
> to understand the (pre-existing) logic in xfs_reflink_zero_posteof.
>
> We obviously need to ensure data between i_size and the end of the
> block that i_size sits in is zeroed (but IIRC we already do that
> in write and truncate anyway). But what is the point of zeroing
> any speculative preallocation beyond the last block that actually
> contains data? Just truncating the preallocation and freeing
> the delalloc and unwritten blocks seems like it would be way
> more efficient.
>
I've had the same idea before, I asked Dave and he explained that Linux
could leak data beyond EOF page for some cases, e.g. mmap() can write to
the EOF page beyond EOF without failing, and the data in that EOF page
could be non-zeroed by mmap(), so the zeroing is still needed now.
OTOH, if we free the delalloc and unwritten blocks beyond EOF blocks, he
said it could lead to some performance problems and make thinks
complicated to deal with the trimming of EOF block. Please see [1]
for details and maybe Dave could explain more.
[1] https://lore.kernel.org/linux-xfs/ZeERAob9Imwh01bG@dread.disaster.area/
Thanks,
Yi.
next prev parent reply other threads:[~2024-04-26 7:18 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-25 13:13 [PATCH v5 0/9] xfs/iomap: fix non-atomic clone operation and don't update size when zeroing range post eof Zhang Yi
2024-04-25 13:13 ` [PATCH v5 1/9] xfs: match lock mode in xfs_buffered_write_iomap_begin() Zhang Yi
2024-04-25 13:13 ` [PATCH v5 2/9] xfs: make the seq argument to xfs_bmapi_convert_delalloc() optional Zhang Yi
2024-04-25 13:13 ` [PATCH v5 3/9] xfs: make xfs_bmapi_convert_delalloc() to allocate the target offset Zhang Yi
2024-04-25 13:13 ` [PATCH v5 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks Zhang Yi
2024-04-25 18:29 ` Darrick J. Wong
2024-04-26 6:24 ` Zhang Yi
2024-04-26 6:33 ` Christoph Hellwig
2024-04-26 7:18 ` Zhang Yi [this message]
2024-04-27 6:59 ` Christoph Hellwig
2024-04-28 3:26 ` Zhang Yi
2024-04-29 4:41 ` Christoph Hellwig
2024-04-29 7:11 ` Zhang Yi
2024-04-25 13:13 ` [PATCH v5 5/9] iomap: drop the write failure handles when unsharing and zeroing Zhang Yi
2024-04-25 13:13 ` [PATCH v5 6/9] iomap: don't increase i_size if it's not a write operation Zhang Yi
2024-04-25 13:13 ` [PATCH v5 7/9] iomap: use a new variable to handle the written bytes in iomap_write_iter() Zhang Yi
2024-04-25 13:13 ` [PATCH v5 8/9] iomap: make iomap_write_end() return a boolean Zhang Yi
2024-04-25 13:13 ` [PATCH v5 9/9] iomap: do some small logical cleanup in buffered write Zhang Yi
-- strict thread matches above, loose matches on Subject: below --
2024-03-20 11:05 [PATCH v4 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks Zhang Yi
2024-04-23 11:17 ` [PATCH v5 " Zhang Yi
2024-04-25 12:22 ` Christoph Hellwig
2024-04-25 12:32 ` Zhang Yi
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