linux-ext4 - Re: [PATCH] ext4: remove unnecessary ext4_inode_datasync

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Message-ID: <01e6abf4-3ae5-ecab-3b7f-876c8a3fcbb4@sjtu.edu.cn>
Date:   Fri, 5 Nov 2021 13:28:10 +0800
From:   Zhongwei Cai <sunrise_l@...u.edu.cn>
To:     Dave Chinner <david@...morbit.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, mingkaidong@...il.com
Subject: Re: [PATCH] ext4: remove unnecessary ext4_inode_datasync_dirty in
 read path

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.