Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock

[Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>]

On Mon, Jan 31, 2022 at 12:09:09PM -0500, Waiman Long wrote:
> On 1/31/22 12:01, Roman Gushchin wrote:
> > On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote:
> > > On 10/1/21 19:51, Roman Gushchin wrote:
> > > > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote:
> > > > > When freeing a page associated with an offlined memcg, refill_stock()
> > > > > will put it into local stock delaying its demise until another memcg
> > > > > comes in to take its place in the stock. To avoid that, we now check
> > > > > for offlined memcg and go directly in this case to the slowpath for
> > > > > the uncharge via the repurposed cancel_charge() function.
> > > > Hi Waiman!
> > > > 
> > > > I'm afraid it can make a cleanup of a dying cgroup slower: for every
> > > > released page we'll potentially traverse the whole cgroup tree and
> > > > decrease atomic page counters.
> > > > 
> > > > I'm not sure I understand the benefits we get from this change which
> > > > do justify the slowdown on the cleanup path.
> > > > 
> > > > Thanks!
> > > I was notified of a lockdep splat that this patch may help to prevent.
> > Would you mind to test this patch:
> > https://www.spinics.net/lists/cgroups/msg31244.html  ?
> > 
> > It should address this dependency.
> 
> Thanks for the pointer. I believe that your patch should be able to address
> this circular locking dependency.
> 
> Feel free to add my
> 
> Reviewed-by: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

Thank you!