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

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Date: Fri, 31 May 2024 08:27:32 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: Zhang Yi <yi.zhang@...weicloud.com>, 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 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?

> > +		/*
> > +		 * 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..."

--D

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