linux-kernel - Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

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Date:   Tue, 22 Oct 2019 10:08:35 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Pingfan Liu <kernelfans@...il.com>, Qian Cai <cai@....pw>,
        Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

On Tue 22-10-19 08:52:28, David Hildenbrand wrote:
> On 21.10.19 19:23, David Hildenbrand wrote:
> > Two cleanups that popped up while working on (and discussing) virtio-mem:
> >   https://lkml.org/lkml/2019/9/19/463
> > 
> > Tested with DIMMs on x86.
> > 
> > As discussed with michal in v1, I'll soon look into removing the use
> > of PG_reserved during memory onlining completely - most probably
> > disallowing to offline memory blocks with holes, cleaning up the
> > onlining+offlining code.
> 
> BTW, I remember that ZONE_DEVICE pages are still required to be set
> PG_reserved. That has to be sorted out first.

Do they?

> I remember that somebody was
> working on it a while ago but didn't hear about that again. Will look into
> that as well - should be as easy as adding a zone check (if there isn't a
> pfn_to_online_page() check already). But of course, there might be special
> cases ....

I remember Alexander didn't want to change the PageReserved handling
because he was worried about unforeseeable side effects. I have a vague
recollection he (or maybe Dan) has promissed some follow up clean ups
which didn't seem to materialize.
-- 
Michal Hocko
SUSE Labs