Re: [PATCH 2/9] blkcg, writeback: Add wbc->no_wbc_acct

From: Tejun Heo
Date: Mon Jun 24 2019 - 08:59:04 EST

Hello, Jan.

On Mon, Jun 24, 2019 at 10:21:30AM +0200, Jan Kara wrote:
> OK, now I understand. Just one more question: So effectively, you are using
> wbc->no_wbc_acct to pass information from btrfs code to btrfs code telling
> it whether IO should or should not be accounted with wbc_account_io().


> Wouldn't it make more sense to just pass this information internally
> within btrfs? Granted, if this mechanism gets more widespread use by other
> filesystems, then probably using wbc flag makes more sense. But I'm not
> sure if this isn't a premature generalization...

The btrfs async issuers end up using generic writeback path and uses
the generic wbc owner mechanisms so that ios are attached to the right
cgroup too. So, I kinda prefer to provide a generic mechanism from
wbc side. That said, the names are a bit misleading and I think it'd
be better to rename them to something more explicit, e.g. sth along
the line of wbc_update_cgroup_owner() and wbc->no_cgroup_owner. What
do you think?