Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout
From: Mike Rapoport
Date: Thu Feb 25 2021 - 13:08:39 EST
On Thu, Feb 25, 2021 at 06:51:53PM +0100, Vlastimil Babka wrote:
>
On 2/24/21 4:39 PM, Mike Rapoport wrote:
>
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>
>
Hi, thanks for your efforts. I'll just nit pick on the description/comments as I
>
don't feel confident about judging the implementation correctness, sorry :)
>
>
> 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 of this page are set to
>
> default values and it 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.
>
>
>
> Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions
>
> rather that check each PFN") the holes inside a zone were re-initialized
>
> during memmap_init() and got their zone/node links right. However, after
>
> that commit nothing updates the struct pages representing such holes.
>
>
>
> 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);
>
>
... in set_pfnblock_flags_mask() when called with a struct page from the
>
"Unknown E820 type" range.
"... in set_pfnblock_flags_mask() when called with a struct page from a range
other than E820_TYPE_RAM"
then :)
>
> because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
>
> in struct page) in the same pageblock.
>
>
I would say "there are apparently pages" ... "and ZONE_DMA does not span this range"
I'd rephrase it differently, something like
"because there are pages in the range of ZONE_DMA32 but the unset zone link
in struct page makes them appear as a part of ZONE_DMA"
>
> Interleave initialization of the unavailable pages with the normal
>
> initialization of memory map, so that zone and node information will be
>
> properly set on struct pages that are not backed by the actual memory.
>
>
>
> With this change the pages for holes inside a zone will get proper
>
> zone/node links and the pages that are not spanned by any node will get
>
> links to the adjacent zone/node.
>
>
What if two zones are adjacent? I.e. if the hole was at a boundary between two
>
zones.
What do you mean by "adjacent zones"? If there is a hole near the zone
boundary, zone span would be clamped to exclude the hole.
>
> Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
>
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>
> Reported-by: Qian Cai <cai@xxxxxx>
>
> Reported-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>
> Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
>
>
For the approach:
>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
>
>
> ---
>
> mm/page_alloc.c | 147 +++++++++++++++++++++---------------------------
>
> 1 file changed, 64 insertions(+), 83 deletions(-)
>
>
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>
> index 3e93f8b29bae..a11a9acde708 100644
>
> --- a/mm/page_alloc.c
>
> +++ b/mm/page_alloc.c
>
> @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone)
>
> }
>
> }
>
>
>
> +#if !defined(CONFIG_FLAT_NODE_MEM_MAP)
>
> +/*
>
> + * Only struct pages that correspond to ranges defined by memblock.memory
>
> + * are zeroed and initialized by going through __init_single_page() during
>
> + * memmap_init_zone().
>
> + *
>
> + * 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
>
>
physical
Thanks.
>
> + * 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
>
> + *
>
> + * Explicitly initialize those struct pages so that:
>
> + * - PG_Reserved is set
>
> + * - zone and node links point to zone and node that span the page
>
>
Yes spanned pages are the most important, but should you also describe here the
>
adjacent ones, as you do in commit log?
Will try :)
>
> + */
>
> +static u64 __meminit init_unavailable_range(unsigned long spfn,
>
> + unsigned long epfn,
>
> + int zone, int node)
>
> +{
>
> + unsigned long pfn;
>
> + u64 pgcnt = 0;
>
> +
>
> + 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;
>
> + }
>
> + __init_single_page(pfn_to_page(pfn), pfn, zone, node);
>
> + __SetPageReserved(pfn_to_page(pfn));
>
> + pgcnt++;
>
> + }
>
> +
>
> + return pgcnt;
>
> +}
>
> +#else
>
> +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
>
> + int zone, int node)
>
> +{
>
> + return 0;
>
> +}
>
> +#endif
>
> +
>
> void __meminit __weak memmap_init_zone(struct zone *zone)
>
> {
>
> unsigned long zone_start_pfn = zone->zone_start_pfn;
>
> unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages;
>
> int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
>
> + static unsigned long hole_pfn = 0;
>
> unsigned long start_pfn, end_pfn;
>
> + u64 pgcnt = 0;
>
>
>
> for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
>
> start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
>
> @@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone)
>
> memmap_init_range(end_pfn - start_pfn, nid,
>
> zone_id, start_pfn, zone_end_pfn,
>
> MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
>
> +
>
> + if (hole_pfn < start_pfn)
>
> + pgcnt += init_unavailable_range(hole_pfn, start_pfn,
>
> + zone_id, nid);
>
> + hole_pfn = end_pfn;
>
> }
>
> +
>
> +#ifdef CONFIG_SPARSEMEM
>
> + end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
>
> + if (hole_pfn < end_pfn)
>
> + pgcnt += init_unavailable_range(hole_pfn, end_pfn,
>
> + zone_id, nid);
>
> +#endif
>
> +
>
> + if (pgcnt)
>
> + pr_info(" %s zone: %lld pages in unavailable ranges\n",
>
> + zone->name, pgcnt);
>
> }
>
>
>
> static int zone_batchsize(struct zone *zone)
>
> @@ -7092,88 +7156,6 @@ void __init free_area_init_memoryless_node(int nid)
>
> free_area_init_node(nid);
>
> }
>
>
>
> -#if !defined(CONFIG_FLAT_NODE_MEM_MAP)
>
> -/*
>
> - * 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)
>
> -{
>
> - unsigned long pfn;
>
> - u64 pgcnt = 0;
>
> -
>
> - 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);
>
> - __SetPageReserved(pfn_to_page(pfn));
>
> - pgcnt++;
>
> - }
>
> -
>
> - return pgcnt;
>
> -}
>
> -
>
> -/*
>
> - * 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.
>
> - *
>
> - * 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.
>
> - */
>
> -static void __init init_unavailable_mem(void)
>
> -{
>
> - phys_addr_t start, end;
>
> - u64 i, pgcnt;
>
> - phys_addr_t next = 0;
>
> -
>
> - /*
>
> - * Loop through unavailable ranges not covered by memblock.memory.
>
> - */
>
> - pgcnt = 0;
>
> - for_each_mem_range(i, &start, &end) {
>
> - if (next < start)
>
> - pgcnt += init_unavailable_range(PFN_DOWN(next),
>
> - PFN_UP(start));
>
> - 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.
>
> - */
>
> - pgcnt += init_unavailable_range(PFN_DOWN(next),
>
> - round_up(max_pfn, PAGES_PER_SECTION));
>
> -
>
> - /*
>
> - * 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);
>
> -}
>
> -#else
>
> -static inline void __init init_unavailable_mem(void)
>
> -{
>
> -}
>
> -#endif /* !CONFIG_FLAT_NODE_MEM_MAP */
>
> -
>
> #if MAX_NUMNODES > 1
>
> /*
>
> * Figure out the number of possible node ids.
>
> @@ -7597,7 +7579,6 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>
> /* Initialise every node */
>
> mminit_verify_pageflags_layout();
>
> setup_nr_node_ids();
>
> - init_unavailable_mem();
>
> for_each_online_node(nid) {
>
> pg_data_t *pgdat = NODE_DATA(nid);
>
> free_area_init_node(nid);
>
>
>
--
Sincerely yours,
Mike.