linux-kernel - Re: [PATCH v7 0/6] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups

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Message-ID: <YLqoJn/FmyqjQs0M@carbon.lan>
Date:   Fri, 4 Jun 2021 15:24:38 -0700
From:   Roman Gushchin <guro@...com>
To:     Tejun Heo <tj@...nel.org>
CC:     Jan Kara <jack@...e.cz>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dennis Zhou <dennis@...nel.org>,
        Dave Chinner <dchinner@...hat.com>, <cgroups@...r.kernel.org>
Subject: Re: [PATCH v7 0/6] cgroup, blkcg: prevent dirty inodes to pin dying
 memory cgroups

On Fri, Jun 04, 2021 at 11:53:02AM -0400, Tejun Heo wrote:
> On Thu, Jun 03, 2021 at 06:31:53PM -0700, Roman Gushchin wrote:
> > To solve the problem inodes should be eventually detached from the
> > corresponding writeback structure. It's inefficient to do it after
> > every writeback completion. Instead it can be done whenever the
> > original memory cgroup is offlined and writeback structure is getting
> > killed. Scanning over a (potentially long) list of inodes and detach
> > them from the writeback structure can take quite some time. To avoid
> > scanning all inodes, attached inodes are kept on a new list (b_attached).
> > To make it less noticeable to a user, the scanning and switching is performed
> > from a work context.
> 
> Sorry for chiming in late but the series looks great to me and the only
> comment I have is the migration target on the last patch, which isn't a
> critical issue. Please feel free to add
> 
>  Acked-by: Tejun Heo <tj@...nel.org>

Thank you for taking a look and for acking the series!

I agree that switching to the nearest ancestor makes sense. If I remember
correctly, I was doing this in v1 (or at least planned to do), but then
switched to zeroing the pointer and then to bdi's wb.

I fixed it in v8 and pushed it here: https://github.com/rgushchin/linux/tree/cgwb.8 .
I'll wait a bit for Jan's and others feedback and will post v8 on Monday.
Hopefully, it will be the final version.

Btw, how are such patches usually routed? Through Jens's tree?

Thanks!