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Subject: Re: [PATCH] ext4: remove unnecessary ext4_inode_datasync_dirty in
 read path
To:     Dave Chinner <david@fromorbit.com>
Cc:     tytso@mit.edu, adilger.kernel@dilger.ca,
        linux-ext4@vger.kernel.org, mingkaidong@gmail.com
References: <20211102024258.210439-1-sunrise_l@sjtu.edu.cn>
 <20211103002843.GC418105@dread.disaster.area>
 <ffb199dc-f7ae-ba03-db57-bf7acc3d0636@sjtu.edu.cn>
 <20211104232226.GD418105@dread.disaster.area>
From:   Zhongwei Cai <sunrise_l@sjtu.edu.cn>
Message-ID: <01e6abf4-3ae5-ecab-3b7f-876c8a3fcbb4@sjtu.edu.cn>
Date:   Fri, 5 Nov 2021 13:28:10 +0800
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On 11/5/21 7:22 AM, Dave Chinner wrote:
> 
> No. Some filesystems don't track inode metadata dirty status using
> the VFS inode; instead they track it more efficiently in internal
> inode and/or journal based structures. Hence the only way to get
> "inode needs journal flush for data stability" information to
> generic IO code is to have a specific per-IO mapping flag for it.
> 

Could we add IOMAP_REPORT_DIRTY flag in the flags field of
struct iomap_iter to indicate whether the IOMAP_F_DIRTY flag
needs to be set or not?

Currently the IOMAP_F_DIRTY flag is only checked in
iomap_swapfile_activate(), dax_iomap_fault() and iomap_dio_rw()
(To be more specific, only the write path in dax_iomap_fault() and
iomap_dio_rw()). So it would be unnecessary to set the IOMAP_F_DIRTY
flag in dax_iomap_rw() called in the previous tests.

Other file systems that set the IOMAP_F_DIRTY flag efficiently
could ignore the IOMAP_REPORT_DIRTY flag.

Best,

Zhongwei.