linux-kernel - Re: [RFC PATCH v4 5/8] xfs: refactor the truncating order

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Date: Mon, 3 Jun 2024 21:51:16 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: "Darrick J. Wong" <djwong@...nel.org>,
 Christoph Hellwig <hch@...radead.org>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, brauner@...nel.org, david@...morbit.com,
 chandanbabu@...nel.org, jack@...e.cz, willy@...radead.org,
 yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [RFC PATCH v4 5/8] xfs: refactor the truncating order

On 2024/5/31 23:27, Darrick J. Wong wrote:
> On Fri, May 31, 2024 at 06:31:36AM -0700, Christoph Hellwig wrote:
>>> +	write_back = newsize > ip->i_disk_size && oldsize != ip->i_disk_size;
>>
>> Maybe need_writeback would be a better name for the variable?  Also no
>> need to initialize it to false at declaration time if it is
>> unconditionally set here.
> 
> This variable captures whether or not we need to write dirty file tail
> data because we're extending the ondisk EOF, right?
> 
> I don't really like long names like any good 1980s C programmer, but
> maybe we should name this something like "extending_ondisk_eof"?
> 
> 	if (newsize > ip->i_disk_size && oldsize != ip->i_disk_size)
> 		extending_ondisk_eof = true;
> 
> 	...
> 
> 	if (did_zeroing || extending_ondisk_eof)
> 		filemap_write_and_wait_range(...);
> 
> Hm?

Sure, this name looks better.

> 
>>> +		/*
>>> +		 * Updating i_size after writing back to make sure the zeroed
>>> +		 * blocks could been written out, and drop all the page cache
>>> +		 * range that beyond blocksize aligned new EOF block.
>>> +		 *
>>> +		 * We've already locked out new page faults, so now we can
>>> +		 * safely remove pages from the page cache knowing they won't
>>> +		 * get refaulted until we drop the XFS_MMAP_EXCL lock after the
> 
> And can we correct the comment here too?
> 
> "...until we drop XFS_MMAPLOCK_EXCL after the extent manipulations..."
> 

Sure,

> --D
> 
>>> +		 * extent manipulations are complete.
>>> +		 */
>>> +		i_size_write(inode, newsize);
>>> +		truncate_pagecache(inode, roundup_64(newsize, blocksize));
>>
>> Any reason this open codes truncate_setsize()?
>>

It's not equal to open codes truncate_setsize(), please look the truncate
start pos is aligned to rtextsize for realtime inode, we only drop page
cache that beyond the new aligned EOF block.

Thanks,
Yi.