linux-kernel - Re: [PATCH v5 2/2] writeback, cgroup: release dying cgwbs by switching attached inodes

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Message-ID: <YLEY1RX3FhR9eWrv@carbon.DHCP.thefacebook.com>
Date:   Fri, 28 May 2021 09:22:45 -0700
From:   Roman Gushchin <guro@...com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        <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 v5 2/2] writeback, cgroup: release dying cgwbs by
 switching attached inodes

On Fri, May 28, 2021 at 10:58:04AM +0800, Ming Lei wrote:
> On Wed, May 26, 2021 at 03:25:57PM -0700, Roman Gushchin wrote:
> > Asynchronously try to release dying cgwbs by switching clean attached
> > inodes to the bdi's wb. It helps to get rid of per-cgroup writeback
> > structures themselves and of pinned memory and block cgroups, which
> > are way larger structures (mostly due to large per-cpu statistics
> > data). It helps to prevent memory waste and different scalability
> > problems caused by large piles of dying cgroups.
> > 
> > A cgwb cleanup operation can fail due to different reasons (e.g. the
> > cgwb has in-glight/pending io, an attached inode is locked or isn't
> > clean, etc). In this case the next scheduled cleanup will make a new
> > attempt. An attempt is made each time a new cgwb is offlined (in other
> > words a memcg and/or a blkcg is deleted by a user). In the future an
> > additional attempt scheduled by a timer can be implemented.
> > 
> > Signed-off-by: Roman Gushchin <guro@...com>
> > ---
> >  fs/fs-writeback.c                | 35 ++++++++++++++++++
> >  include/linux/backing-dev-defs.h |  1 +
> >  include/linux/writeback.h        |  1 +
> >  mm/backing-dev.c                 | 61 ++++++++++++++++++++++++++++++--
> >  4 files changed, 96 insertions(+), 2 deletions(-)
> > 
> 
> Hello Roman,
> 
> The following kernel panic is triggered by this patch:

Hello Ming!

Thank you for the report and for trying my patches!
I think I know what it is and will fix in the next version.

Thanks!