Re: [PATCH v3 2/2] mm: fix initialization of struct page for holes in memory layout

[Baoquan He <bhe@redhat.com>]

On 02/01/21 at 10:14am, David Hildenbrand wrote:
> On 11.01.21 20:40, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > There could be struct pages that are not backed by actual physical memory.
> > This can happen when the actual memory bank is not a multiple of
> > SECTION_SIZE or when an architecture does not register memory holes
> > reserved by the firmware as memblock.memory.
> > 
> > Such pages are currently initialized using init_unavailable_mem() function
> > that iterates through PFNs in holes in memblock.memory and if there is a
> > struct page corresponding to a PFN, the fields if this page are set to
> > default values and the page is marked as Reserved.
> > 
> > init_unavailable_mem() does not take into account zone and node the page
> > belongs to and sets both zone and node links in struct page to zero.
> > 
> > On a system that has firmware reserved holes in a zone above ZONE_DMA, for
> > instance in a configuration below:
> > 
> > 	# grep -A1 E820 /proc/iomem
> > 	7a17b000-7a216fff : Unknown E820 type
> > 	7a217000-7bffffff : System RAM
> > 
> > unset zone link in struct page will trigger
> > 
> > 	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
> > 
> > because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in
> > struct page) in the same pageblock.
> > 
> > Update init_unavailable_mem() to use zone constraints defined by an
> > architecture to properly setup the zone link and use node ID of the
> > adjacent range in memblock.memory to set the node link.
> > 
> > Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
> > Reported-by: Andrea Arcangeli <aarcange@redhat.com>
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> >   mm/page_alloc.c | 84 +++++++++++++++++++++++++++++--------------------
> >   1 file changed, 50 insertions(+), 34 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index bdbec4c98173..0b56c3ca354e 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7077,23 +7077,26 @@ void __init free_area_init_memoryless_node(int nid)
> >    * Initialize all valid struct pages in the range [spfn, epfn) and mark them
> >    * PageReserved(). Return the number of struct pages that were initialized.
> >    */
> > -static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn)
> > +static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn,
> > +					 int zone, int nid)
> >   {
> > -	unsigned long pfn;
> > +	unsigned long pfn, zone_spfn, zone_epfn;
> >   	u64 pgcnt = 0;
> > +	zone_spfn = arch_zone_lowest_possible_pfn[zone];
> > +	zone_epfn = arch_zone_highest_possible_pfn[zone];
> > +
> > +	spfn = clamp(spfn, zone_spfn, zone_epfn);
> > +	epfn = clamp(epfn, zone_spfn, zone_epfn);
> > +
> >   	for (pfn = spfn; pfn < epfn; pfn++) {
> >   		if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
> >   			pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
> >   				+ pageblock_nr_pages - 1;
> >   			continue;
> >   		}
> > -		/*
> > -		 * Use a fake node/zone (0) for now. Some of these pages
> > -		 * (in memblock.reserved but not in memblock.memory) will
> > -		 * get re-initialized via reserve_bootmem_region() later.
> > -		 */
> > -		__init_single_page(pfn_to_page(pfn), pfn, 0, 0);
> > +
> > +		__init_single_page(pfn_to_page(pfn), pfn, zone, nid);
> >   		__SetPageReserved(pfn_to_page(pfn));
> >   		pgcnt++;
> >   	}
> > @@ -7102,51 +7105,64 @@ static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn)
> >   }
> >   /*
> > - * Only struct pages that are backed by physical memory are zeroed and
> > - * initialized by going through __init_single_page(). But, there are some
> > - * struct pages which are reserved in memblock allocator and their fields
> > - * may be accessed (for example page_to_pfn() on some configuration accesses
> > - * flags). We must explicitly initialize those struct pages.
> > + * Only struct pages that correspond to ranges defined by memblock.memory
> > + * are zeroed and initialized by going through __init_single_page() during
> > + * memmap_init().
> > + *
> > + * But, there could be struct pages that correspond to holes in
> > + * memblock.memory. This can happen because of the following reasons:
> > + * - phyiscal memory bank size is not necessarily the exact multiple of the
> > + *   arbitrary section size
> > + * - early reserved memory may not be listed in memblock.memory
> > + * - memory layouts defined with memmap= kernel parameter may not align
> > + *   nicely with memmap sections
> >    *
> > - * This function also addresses a similar issue where struct pages are left
> > - * uninitialized because the physical address range is not covered by
> > - * memblock.memory or memblock.reserved. That could happen when memblock
> > - * layout is manually configured via memmap=, or when the highest physical
> > - * address (max_pfn) does not end on a section boundary.
> > + * Explicitly initialize those struct pages so that:
> > + * - PG_Reserved is set
> > + * - zone link is set accorging to the architecture constrains
> > + * - node is set to node id of the next populated region except for the
> > + *   trailing hole where last node id is used
> >    */
> > -static void __init init_unavailable_mem(void)
> > +static void __init init_zone_unavailable_mem(int zone)
> >   {
> > -	phys_addr_t start, end;
> > -	u64 i, pgcnt;
> > -	phys_addr_t next = 0;
> > +	unsigned long start, end;
> > +	int i, nid;
> > +	u64 pgcnt;
> > +	unsigned long next = 0;
> >   	/*
> > -	 * Loop through unavailable ranges not covered by memblock.memory.
> > +	 * Loop through holes in memblock.memory and initialize struct
> > +	 * pages corresponding to these holes
> >   	 */
> >   	pgcnt = 0;
> > -	for_each_mem_range(i, &start, &end) {
> > +	for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid) {
> >   		if (next < start)
> > -			pgcnt += init_unavailable_range(PFN_DOWN(next),
> > -							PFN_UP(start));
> > +			pgcnt += init_unavailable_range(next, start, zone, nid);
> >   		next = end;
> >   	}
> >   	/*
> > -	 * Early sections always have a fully populated memmap for the whole
> > -	 * section - see pfn_valid(). If the last section has holes at the
> > -	 * end and that section is marked "online", the memmap will be
> > -	 * considered initialized. Make sure that memmap has a well defined
> > -	 * state.
> > +	 * Last section may surpass the actual end of memory (e.g. we can
> > +	 * have 1Gb section and 512Mb of RAM pouplated).
> > +	 * Make sure that memmap has a well defined state in this case.
> >   	 */
> > -	pgcnt += init_unavailable_range(PFN_DOWN(next),
> > -					round_up(max_pfn, PAGES_PER_SECTION));
> > +	end = round_up(max_pfn, PAGES_PER_SECTION);
> > +	pgcnt += init_unavailable_range(next, end, zone, nid);
> >   	/*
> >   	 * Struct pages that do not have backing memory. This could be because
> >   	 * firmware is using some of this memory, or for some other reasons.
> >   	 */
> >   	if (pgcnt)
> > -		pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
> > +		pr_info("Zone %s: zeroed struct page in unavailable ranges: %lld pages", zone_names[zone], pgcnt);
> > +}
> > +
> > +static void __init init_unavailable_mem(void)
> > +{
> > +	int zone;
> > +
> > +	for (zone = 0; zone < ZONE_MOVABLE; zone++)
> > +		init_zone_unavailable_mem(zone);
> 
> Why < ZONE_MOVABLE?
> 
> I remember we can have memory holes inside the movable zone when messing
> with "movablecore" cmdline parameter.

Maybe because we haven't initialized MOABLE zone info at this time.