linux-kernel - Re: [PATCH] mm, memory_hotplug: teach has_unmovable

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Date:   Mon, 5 Nov 2018 18:10:02 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Stable tree <stable@...r.kernel.org>
Subject: Re: [PATCH] mm, memory_hotplug: teach has_unmovable_pages about of
 LRU migrateable pages

On Mon 05-11-18 22:23:08, Baoquan He wrote:
> On 11/05/18 at 01:38pm, Michal Hocko wrote:
> > On Mon 05-11-18 18:25:20, Baoquan He wrote:
> > > Hi Michal,
> > > 
> > > On 11/05/18 at 10:28am, Michal Hocko wrote:
> > > > 
> > > > Or something like this. Ugly as hell, no question about that. I also
> > > > have to think about this some more to convince myself this will not
> > > > result in an endless loop under some situations.
> > > 
> > > It failed. Paste the log and patch diff here, please help check if I made
> > > any mistake on manual code change. The log is at bottom.
> > 
> > The retry patch is obviously still racy, it just makes the race window
> > slightly smaller and I hoped it would catch most of those races but this
> > is obviously not the case.
> > 
> > I was thinking about your MIGRATE_MOVABLE check some more and I still do
> > not like it much, we just change migrate type at many places and I have
> > hard time to actually see this is always safe wrt. to what we need here.
> > 
> > We should be able to restore the zone type check though. The
> > primary problem fixed by 15c30bc09085 ("mm, memory_hotplug: make
> > has_unmovable_pages more robust") was that early allocations made it to
> > the zone_movable range. If we add the check _after_ the PageReserved()
> > check then we should be able to rule all bootmem allocation out.
> > 
> > So what about the following (on top of the previous patch which makes
> > sense on its own I believe).
> 
> Yes, I think this looks very reasonable and should be robust.
> 
> Have tested it, hot removing 4 hotpluggable nodes continusously
> succeeds, and then hot adding them back, still works well.
> 
> So please feel free to add my Tested-by or Acked-by.
> 
> Tested-by: Baoquan He <bhe@...hat.com>
> or
> Acked-by: Baoquan He <bhe@...hat.com>

Thanks for retesting! Does this apply to both patches?
-- 
Michal Hocko
SUSE Labs