linux-ext4 - Re: [PATCH] ext4: Speedup WB_SYNC

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Message-ID: <20140304155443.GD23106@thunk.org>
Date:	Tue, 4 Mar 2014 10:54:43 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Speedup WB_SYNC_ALL pass

On Mon, Mar 03, 2014 at 11:53:28PM +0100, Jan Kara wrote:
> When doing filesystem wide sync, there's no need to force transaction
> commit (or synchronously write inode buffer) separately for each inode
> because ext4_sync_fs() takes care of forcing commit at the end (VFS
> takes care of flushing buffer cache, respectively). Most of the time
> this slowness doesn't manifest because previous WB_SYNC_NONE writeback
> doesn't leave much to write but when there are processes aggressively
> creating new files and several filesystems to sync, the sync slowness
> can be noticeable. In the following test script sync(1) takes around 6
> minutes when there are two ext4 filesystems mounted on a standard SATA
> drive. After this patch sync takes a couple of seconds so we have about
> two orders of magnitude improvement.
> 
>       function run_writers
>       {
>         for (( i = 0; i < 10; i++ )); do
>           mkdir $1/dir$i
>           for (( j = 0; j < 40000; j++ )); do
>             dd if=/dev/zero of=$1/dir$i/$j bs=4k count=4 &>/dev/null
>           done &
>         done
>       }
> 
>       for dir in "$@"; do
>         run_writers $dir
>       done
> 
>       sleep 40
>       time sync
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

Looks good, thanks for the patch!

						- Ted
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