linux-ext4 - Re: [PATCH 0/3] Revert parallel dio reads

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Message-ID: <20190827115118.GY7777@dread.disaster.area>
Date:   Tue, 27 Aug 2019 21:51:18 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Joseph Qi <joseph.qi@...ux.alibaba.com>
Cc:     Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger@...ger.ca>,
        Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 0/3] Revert parallel dio reads

On Tue, Aug 27, 2019 at 10:05:49AM +0800, Joseph Qi wrote:
> This patch set is trying to revert parallel dio reads feature at present
> since it causes significant performance regression in mixed random
> read/write scenario.
> 
> Joseph Qi (3):
>   Revert "ext4: remove EXT4_STATE_DIOREAD_LOCK flag"
>   Revert "ext4: fix off-by-one error when writing back pages before dio
>     read"
>   Revert "ext4: Allow parallel DIO reads"
> 
>  fs/ext4/ext4.h        | 17 +++++++++++++++++
>  fs/ext4/extents.c     | 19 ++++++++++++++-----
>  fs/ext4/inode.c       | 47 +++++++++++++++++++++++++++++++----------------
>  fs/ext4/ioctl.c       |  4 ++++
>  fs/ext4/move_extent.c |  4 ++++
>  fs/ext4/super.c       | 12 +++++++-----
>  6 files changed, 77 insertions(+), 26 deletions(-)

Before doing this, you might want to have a chat and co-ordinate
with the folks that are currently trying to port the ext4 direct IO
code to use the iomap infrastructure:

https://lore.kernel.org/linux-ext4/20190827095221.GA1568@poseidon.bobrowski.net/T/#t

That is going to need the shared locking on read and will work just
fine with shared locking on write, too (it's the code that XFS uses
for direct IO). So it might be best here if you work towards shared
locking on the write side rather than just revert the shared locking
on the read side....

Cheers,

Dave,
-- 
Dave Chinner
david@...morbit.com