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

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Date:   Tue, 6 Nov 2018 17:36:45 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
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 11/06/18 at 05:16pm, Baoquan He wrote:
> On 11/06/18 at 09:28am, Michal Hocko wrote:
> > > > > > > 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?
> > > 
> > > Sorry, don't get it. I just applied this on top of linus's tree and
> > > tested. Do you mean applying it on top of previous code change?
> > 
> > Yes. While the first patch will obviously not help for movable zone
> > because the movable check will override any later check it
> > seems still useful to reduce false positives on normal zones.
> 
> Hmm, I don't know if it will bring a little bit confusion on code
> understanding. Since we only recognize the movable zone issue, and I can
> only reproduce and verify it on the movable zone issue with the movable
> zone check adding.
> 
> Not sure if there are any scenario or use cases to cover those newly added
> checking other movable zone checking. Surely, I have no objection to
		^ than
> adding them. But the two patches are separate issues, they have no
> dependency on each other.
> 
> I just tested the movable zone checking yesterday, will add your
> previous check back, then test again. I believe the result will be
> positive. Will udpate once done.
> 
> Thanks
> Baoquan