linux-kernel - Re: [PATCH] ovl: skip overlayfs superblocks at global sync

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Message-ID: <20200411222829.GO10737@dread.disaster.area>
Date:   Sun, 12 Apr 2020 08:28:29 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-fsdevel@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
        linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-unionfs@...r.kernel.org,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: Re: [PATCH] ovl: skip overlayfs superblocks at global sync

On Thu, Apr 09, 2020 at 11:29:47AM +0300, Konstantin Khlebnikov wrote:
> Stacked filesystems like overlayfs has no own writeback, but they have to
> forward syncfs() requests to backend for keeping data integrity.
> 
> During global sync() each overlayfs instance calls method ->sync_fs()
> for backend although it itself is in global list of superblocks too.
> As a result one syscall sync() could write one superblock several times
> and send multiple disk barriers.
> 
> This patch adds flag SB_I_SKIP_SYNC into sb->sb_iflags to avoid that.

Why wouldn't you just remove the ->sync_fs method from overlay?

I mean, if you don't need the filesystem to do anything special for
one specific data integrity sync_fs call, you don't need it for any
of them, yes?

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