Re: [RFC PATCH v3 07/26] iomap: don't increase i_size if it's not a write operation

From: Dave Chinner <david@fromorbit.com>
To: Zhang Yi <yi.zhang@huaweicloud.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org, tytso@mit.edu,
	adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com,
	djwong@kernel.org, willy@infradead.org, zokeefe@google.com,
	yi.zhang@huawei.com, chengzhihao1@huawei.com, yukuai3@huawei.com,
	wangkefeng.wang@huawei.com
Subject: Re: [RFC PATCH v3 07/26] iomap: don't increase i_size if it's not a write operation
Date: Mon, 19 Feb 2024 10:30:30 +1100	[thread overview]
Message-ID: <ZdKTFp4v1kQuLg9e@dread.disaster.area> (raw)
In-Reply-To: <74ab3c3e-3daf-5374-75e5-bcb25ffdb527@huaweicloud.com>

On Sat, Feb 17, 2024 at 04:55:51PM +0800, Zhang Yi wrote:
> On 2024/2/13 13:46, Christoph Hellwig wrote:
> > Wouldn't it make more sense to just move the size manipulation to the
> > write-only code?  An untested version of that is below.  With this
> 
> Sorry for the late reply and thanks for your suggestion, The reason why
> I introduced this new helper iomap_write_end_simple() is I don't want to
> open code __iomap_put_folio() in each caller since corresponding to
> iomap_write_begin(), it's the responsibility for iomap_write_end_*() to
> put and unlock folio, so I'd like to keep it in iomap_write_end_*().

Just because we currently put the folio in iomap_write_end_*(), it
doesn't mean we must always do it that way.

> But I don't feel strongly about it, it's also fine by me to just move
> the size manipulation to the write-only code if you think it's better.

I agree with Christoph that it's better to move the i_size update
into iomap_write_iter() than it is to implement a separate write_end
function that does not update the i_size. The iter functions already
do work directly on the folio that iomap_write_begin() returns, so
having them drop the folio when everything is done isn't a huge
deal...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com