linux-kernel - Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online

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Date:   Fri, 14 Jun 2019 11:03:55 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Qian Cai <cai@....pw>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()

On Fri, Jun 14, 2019 at 7:59 AM Qian Cai <cai@....pw> wrote:
>
> On Fri, 2019-06-14 at 14:28 +0530, Aneesh Kumar K.V wrote:
> > Qian Cai <cai@....pw> writes:
> >
> >
> > > 1) offline is busted [1]. It looks like test_pages_in_a_zone() missed the
> > > same
> > > pfn_section_valid() check.
> > >
> > > 2) powerpc booting is generating endless warnings [2]. In
> > > vmemmap_populated() at
> > > arch/powerpc/mm/init_64.c, I tried to change PAGES_PER_SECTION to
> > > PAGES_PER_SUBSECTION, but it alone seems not enough.
> > >
> >
> > Can you check with this change on ppc64.  I haven't reviewed this series yet.
> > I did limited testing with change . Before merging this I need to go
> > through the full series again. The vmemmap poplulate on ppc64 needs to
> > handle two translation mode (hash and radix). With respect to vmemap
> > hash doesn't setup a translation in the linux page table. Hence we need
> > to make sure we don't try to setup a mapping for a range which is
> > arleady convered by an existing mapping.
>
> It works fine.

Strange... it would only change behavior if valid_section() is true
when pfn_valid() is not or vice versa. They "should" be identical
because subsection-size == section-size on PowerPC, at least with the
current definition of SUBSECTION_SHIFT. I suspect maybe
free_area_init_nodes() is too late to call subsection_map_init() for
PowerPC.