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

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Message-ID: <CAPcyv4i5iUop_H-Ai4q_hn2-3L6aRuovY44tuV50bp1oZj29TQ@mail.gmail.com>
Date:   Fri, 14 Jun 2019 12:48:28 -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 12:40 PM Qian Cai <cai@....pw> wrote:
>
> On Fri, 2019-06-14 at 11:57 -0700, Dan Williams wrote:
> > On Fri, Jun 14, 2019 at 11:03 AM Dan Williams <dan.j.williams@...el.com>
> > wrote:
> > >
> > > 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.
> >
> > Can you give the attached incremental patch a try? This will break
> > support for doing sub-section hot-add in a section that was only
> > partially populated early at init, but that can be repaired later in
> > the series. First things first, don't regress.
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 874eb22d22e4..520c83aa0fec 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7286,12 +7286,10 @@ void __init free_area_init_nodes(unsigned long
> > *max_zone_pfn)
> >
> >         /* Print out the early node map */
> >         pr_info("Early memory node ranges\n");
> > -       for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
> > +       for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid)
> >                 pr_info("  node %3d: [mem %#018Lx-%#018Lx]\n", nid,
> >                         (u64)start_pfn << PAGE_SHIFT,
> >                         ((u64)end_pfn << PAGE_SHIFT) - 1);
> > -               subsection_map_init(start_pfn, end_pfn - start_pfn);
> > -       }
> >
> >         /* Initialise every node */
> >         mminit_verify_pageflags_layout();
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 0baa2e55cfdd..bca8e6fa72d2 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -533,6 +533,7 @@ static void __init sparse_init_nid(int nid,
> > unsigned long pnum_begin,
> >                 }
> >                 check_usemap_section_nr(nid, usage);
> >                 sparse_init_one_section(__nr_to_section(pnum), pnum,
> > map, usage);
> > +               subsection_map_init(section_nr_to_pfn(pnum),
> > PAGES_PER_SECTION);
> >                 usage = (void *) usage + mem_section_usage_size();
> >         }
> >         sparse_buffer_fini();
>
> It works fine except it starts to trigger slab debugging errors during boot. Not
> sure if it is related yet.

If you want you can give this branch a try if you suspect something
else in -next is triggering the slab warning.

https://git.kernel.org/pub/scm/linux/kernel/git/djbw/nvdimm.git/log/?h=subsection-v9

It's the original v9 patchset + dependencies backported to v5.2-rc4.

I otherwise don't see how subsections would effect slab caches.