linux-kernel - Re: [RFC PATCH V4] iomap: add support to track dirty state of sub pages

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Message-ID: <7b160e03-28b8-32b0-244c-bfa7f4127434@huawei.com>
Date:   Fri, 25 Sep 2020 10:30:22 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <hch@...radead.org>, <darrick.wong@...cle.com>,
        <david@...morbit.com>, <linux-xfs@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>
Subject: Re: [RFC PATCH V4] iomap: add support to track dirty state of sub
 pages


On 2020/09/11 20:05, Matthew Wilcox wrote:
>> @@ -683,7 +736,7 @@ static size_t __iomap_write_end(struct inode *inode,
>> loff_t pos, size_t len,
>>   	if (unlikely(copied < len && !PageUptodate(page)))
>>   		return 0;
>>   	iomap_set_range_uptodate(page, offset_in_page(pos), len);
>> -	iomap_set_page_dirty(page);
>> +	iomap_set_range_dirty(page, offset_in_page(pos), len);
> I_think_  the call to set_range_uptodate here is now unnecessary.  The
> blocks should already have been set uptodate in write_begin.  But please
> check!

Hi, Matthew

Sorry it took me so long to get back to this.

I found that set_range_uptodate() might be skipped in write_begin()
in this case:

                  if (!(flags & IOMAP_WRITE_F_UNSHARE) &&
                   ┊   (from <= poff || from >= poff + plen) &&
                   ┊   (to <= poff || to >= poff + plen))
                           continue;

And iomap_adjust_read_range() can set 'poff' greater than 'from'
and 'poff + len' less than 'to'.

Thanks
Yu Kuai