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Date:   Wed, 2 Nov 2022 18:47:21 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Yang Shi <shy828301@gmail.com>
Cc:     Zach O'Keefe <zokeefe@google.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: don't warn if the node is offlined
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On Wed 02-11-22 10:36:07, Yang Shi wrote:
> On Wed, Nov 2, 2022 at 9:15 AM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Wed 02-11-22 09:03:57, Yang Shi wrote:
> > > On Wed, Nov 2, 2022 at 12:39 AM Michal Hocko <mhocko@suse.com> wrote:
> > > >
> > > > On Tue 01-11-22 12:13:35, Zach O'Keefe wrote:
> > > > [...]
> > > > > This is slightly tangential - but I don't want to send a new mail
> > > > > about it -- but I wonder if we should be doing __GFP_THISNODE +
> > > > > explicit node vs having hpage_collapse_find_target_node() set a
> > > > > nodemask. We could then provide fallback nodes for ties, or if some
> > > > > node contained > some threshold number of pages.
> > > >
> > > > I would simply go with something like this (not even compile tested):
> > >
> > > Thanks, Michal. It is definitely an option. As I talked with Zach, I'm
> > > not sure whether it is worth making the code more complicated for such
> > > micro optimization or not. Removing __GFP_THISNODE or even removing
> > > the node balance code should be fine too IMHO. TBH I doubt there would
> > > be any noticeable difference.
> >
> > I do agree that an explicit nodes (quasi)round robin sounds over
> > engineered. It makes some sense to try to target the prevalent node
> > though because this code can be executed from khugepaged and therefore
> > allocating with a completely different affinity than the original fault.
> 
> Yeah, the corner case comes from the node balance code, it just tries
> to balance between multiple prevalent nodes, so you agree to remove it
> IIRC?

Yeah, let's just collect all good nodes into a nodemask and keep
__GFP_THISNODE in place. You can consider having the nodemask per collapse_control
so that you allocate it only once in the struct lifetime.

And as mentioned in other reply it would be really nice to hide this
under CONFIG_NUMA (in a standalong follow up of course).

-- 
Michal Hocko
SUSE Labs