linux-kernel - Re: [PATCH v2 4/6] iomap: correct the dirty length in page mkwrite

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Message-ID: <1728decf-2e29-1b79-f58b-388e671f5da2@huaweicloud.com>
Date: Fri, 16 Aug 2024 10:19:24 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, djwong@...nel.org, brauner@...nel.org,
 david@...morbit.com, jack@...e.cz, willy@...radead.org, yi.zhang@...wei.com,
 chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 4/6] iomap: correct the dirty length in page mkwrite

On 2024/8/15 13:59, Christoph Hellwig wrote:
> On Wed, Aug 14, 2024 at 03:49:41PM +0800, Zhang Yi wrote:
>> Sorry, this makes me confused. How does this could prevent setting
>> redundant dirty bits?
>>
>> Suppose we have a 3K regular file on a filesystem with 1K block size.
>> In iomap_page_mkwrite(), the iter.len is 3K, if the folio size is 4K,
>> folio_mark_dirty() will also mark all 4 bits of ifs dirty. And then,
>> if we expand this file size to 4K, and this will still lead to a hole
>> with dirty bit set but without any block allocated/reserved. Am I
>> missing something?
> 
> No, we still need the ifs manipulation in the loop indeed.  But
> the filemap_dirty_folio (and the not uptodate warning) can still
> move outside the iterator.
> 
Yes, right, I misunderstood.

Thanks,
Yi.