[PATCH v7 0/1] mm: fix initialization of struct page for holes in memory layout

[PATCH v7 0/1] mm: fix initialization of struct page for holes in memory layout

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

Hi,

@Andrew, this is based on v5.11-mmotm-2021-02-18-18-29 with the previous
version reverted

Commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather
that check each PFN") exposed several issues with the memory map
initialization and these patches fix those issues.

Initially there were crashes during compaction that Qian Cai reported back
in April [1]. It seemed back then that the problem was fixed, but a few
weeks ago Andrea Arcangeli hit the same bug [2] and there was an additional
discussion at [3].

I didn't appreciate variety of ways BIOSes can report memory in the first
megabyte, so previous versions of this set caused all kinds of troubles.

The last version that implicitly extended node/zone to cover the complete
section might also have unexpected side effects, so this time I'm trying to
move in forward in baby steps.

This is mostly a return to the fist version that simply merges
init_unavailable_pages() into memmap_init() so that the only effective
change would be more sensible zone/node links in unavailable struct pages.

For now, I've dropped the patch that tried to make ZONE_DMA to span pfn 0
because it didn't cause any issues for really long time and there are way
to many hidden mines around this.

I have an ugly workaround for "pfn 0" issue that IMHO is the safest way to
deal with it until it could be gradually fixed properly:

https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/commit/?h=meminit/pfn0&id=90272f37151c6e1bc2610997310c51f4e984cf2f

v7:
* add handling of section end that span beyond the populated zones

v6: https://lore.kernel.org/lkml/20210222105728.28636-1-rppt@kernel.org
* only interleave initialization of unavailable pages in memmap_init(), so
that it is essentially includes init_unavailable_pages().

v5: https://lore.kernel.org/lkml/20210208110820.6269-1-rppt@kernel.org
* extend node/zone spans to cover complete sections, this allows to interleave
  the initialization of unavailable pages with "normal" memory map init.
* drop modifications to x86 early setup

v4: https://lore.kernel.org/lkml/20210130221035.4169-1-rppt@kernel.org/
* make sure pages in the range 0 - start_pfn_of_lowest_zone are initialized
  even if an architecture hides them from the generic mm
* finally make pfn 0 on x86 to be a part of memory visible to the generic
  mm as reserved memory.

v3: https://lore.kernel.org/lkml/20210111194017.22696-1-rppt@kernel.org
* use architectural zone constraints to set zone links for struct pages
  corresponding to the holes
* drop implicit update of memblock.memory
* add a patch that sets pfn 0 to E820_TYPE_RAM on x86

v2: https://lore.kernel.org/lkml/20201209214304.6812-1-rppt@kernel.org/):
* added patch that adds all regions in memblock.reserved that do not
overlap with memblock.memory to memblock.memory in the beginning of
free_area_init()

[1] https://lore.kernel.org/lkml/8C537EB7-85EE-4DCF-943E-3CC0ED0DF56D@lca.pw
[2] https://lore.kernel.org/lkml/20201121194506.13464-1-aarcange@redhat.com
[3] https://lore.kernel.org/mm-commits/20201206005401.qKuAVgOXr%akpm@linux-foundation.org

Mike Rapoport (1):
  mm/page_alloc.c: refactor initialization of struct page for holes in
    memory layout

 mm/page_alloc.c | 147 +++++++++++++++++++++---------------------------
 1 file changed, 64 insertions(+), 83 deletions(-)

-- 
2.28.0

[PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Mike Rapoport]

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 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);

because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
in struct page) in the same pageblock.

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.

Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reported-by: Qian Cai <cai@lca.pw>
Reported-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
---
 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
+ *   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
+ */
+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);
-- 
2.28.0

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[David Hildenbrand]

On 24.02.21 16:39, 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 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);
> 
> because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
> in struct page) in the same pageblock.
> 
> 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.
> 
> Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Reported-by: Qian Cai <cai@lca.pw>
> Reported-by: Andrea Arcangeli <aarcange@redhat.com>
> Reviewed-by: Baoquan He <bhe@redhat.com>
> ---
>   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
> + *   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
> + */
> +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);

We might still double-initialize PFNs when two zones overlap within a 
section, correct? This might worth documenting - also, you might want to 
take some of the original comment the accompanied this code.

You should also document (in the patch description?) that node/zone 
spans are not properly handled yet for such hole pfns and that this 
might require care in the future.


I played a little with weird setups and expected the memap state using 
page-types (well, I can't inspect the node/zone that way but at least 
have a look if the memmap was initialized). No surprises.

-- 
Thanks,

David / dhildenb

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Mike Rapoport]

On Thu, Feb 25, 2021 at 04:59:06PM +0100, David Hildenbrand wrote:
> On 24.02.21 16:39, 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 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);
> > 
> > because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
> > in struct page) in the same pageblock.
> > 
> > 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.
> > 
> > Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > Reported-by: Qian Cai <cai@lca.pw>
> > Reported-by: Andrea Arcangeli <aarcange@redhat.com>
> > Reviewed-by: Baoquan He <bhe@redhat.com>
> > ---
> >   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
> > + *   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
> > + */
> > +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);
> 
> We might still double-initialize PFNs when two zones overlap within a
> section, correct?

You mean that a section crosses zones boundary?
I don't think it's that important.

> This might worth documenting - also, you might want to
> take some of the original comment the accompanied this code.

The original comment was not exactly right, I believe the comment above
init_unavailable_range() better describes what's going on there.
 
> You should also document (in the patch description?) that node/zone spans
> are not properly handled yet for such hole pfns and that this might require
> care in the future.

I think Link: will suffice for this.
 
> I played a little with weird setups and expected the memap state using
> page-types (well, I can't inspect the node/zone that way but at least have a
> look if the memmap was initialized). No surprises.

Great, thanks!

-- 
Sincerely yours,
Mike.

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Vlastimil Babka]

On 2/24/21 4:39 PM, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>

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.

> 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"

> 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.

> Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Reported-by: Qian Cai <cai@lca.pw>
> Reported-by: Andrea Arcangeli <aarcange@redhat.com>
> Reviewed-by: Baoquan He <bhe@redhat.com>

For the approach:
Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  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

> + *   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?

> + */
> +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);
> 

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[David Hildenbrand]

On 25.02.21 18:06, Mike Rapoport wrote:
> On Thu, Feb 25, 2021 at 04:59:06PM +0100, David Hildenbrand wrote:
>> On 24.02.21 16:39, 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 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);
>>>
>>> because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
>>> in struct page) in the same pageblock.
>>>
>>> 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.
>>>
>>> Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>>> Reported-by: Qian Cai <cai@lca.pw>
>>> Reported-by: Andrea Arcangeli <aarcange@redhat.com>
>>> Reviewed-by: Baoquan He <bhe@redhat.com>
>>> ---
>>>    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
>>> + *   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
>>> + */
>>> +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);
>>
>> We might still double-initialize PFNs when two zones overlap within a
>> section, correct?
> 
> You mean that a section crosses zones boundary?
> I don't think it's that important.
> 
>> This might worth documenting - also, you might want to
>> take some of the original comment the accompanied this code.
> 
> The original comment was not exactly right, I believe the comment above
> init_unavailable_range() better describes what's going on there.

Ah, okay - as long as it's documented I'm happy :)

-- 
Thanks,

David / dhildenb

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Linus Torvalds]

On Thu, Feb 25, 2021 at 9:07 AM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> >
> > We might still double-initialize PFNs when two zones overlap within a
> > section, correct?
>
> You mean that a section crosses zones boundary?
> I don't think it's that important.

What if there was a memory allocation in between that could allocate
the once-initialized page?

Maybe it can't happen, or is not an issue for some other reason, but
this code has been fragile and had a ton of subtle issues, so maybe
worth documenting (or explaining here why it's just not relevant)

          Linus

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Mike Rapoport]

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@linux.ibm.com>
> 
> 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@linux.ibm.com>
> > Reported-by: Qian Cai <cai@lca.pw>
> > Reported-by: Andrea Arcangeli <aarcange@redhat.com>
> > Reviewed-by: Baoquan He <bhe@redhat.com>
> 
> For the approach:
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> > ---
> >  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.

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Mike Rapoport]

On Thu, Feb 25, 2021 at 09:54:34AM -0800, Linus Torvalds wrote:
> On Thu, Feb 25, 2021 at 9:07 AM Mike Rapoport <rppt@linux.ibm.com> wrote:
> >
> > >
> > > We might still double-initialize PFNs when two zones overlap within a
> > > section, correct?
> >
> > You mean that a section crosses zones boundary?
> > I don't think it's that important.
> 
> What if there was a memory allocation in between that could allocate
> the once-initialized page?

Can't happen because this code runs before any allocation is possible and
it is single threaded.
 
> Maybe it can't happen, or is not an issue for some other reason, but
> this code has been fragile and had a ton of subtle issues, so maybe
> worth documenting (or explaining here why it's just not relevant)

Ok, I'll do another pass on the comments in the code.

>           Linus

-- 
Sincerely yours,
Mike.

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Vlastimil Babka]

On 2/25/21 7:05 PM, Mike Rapoport wrote:
> On Thu, Feb 25, 2021 at 06:51:53PM +0100, Vlastimil Babka wrote:
>> > 
>> > 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 :)

Better :)

>> > 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"

Much better, thanks!

>> > 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.

Yeah, zone span should exclude those pages, but you still somehow handle them?
That's how I read "pages that are not spanned by any node will get links to the
adjacent zone/node."
So is it always a unique zone/node can be determined?

Let's say we have:

<memory on node 0>
---- pageblock boundary ----
<more memory on node 0>
<a hole>
<memory on node 1>
---- pageblock boundary ----

Now I hope such configurations don't really exist :) But if we simulated them in
QEMU, what would be the linkage in struct pages in that hole?

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Mike Rapoport]

On Thu, Feb 25, 2021 at 07:38:44PM +0100, Vlastimil Babka wrote:
> On 2/25/21 7:05 PM, Mike Rapoport wrote:
> >> 
> >> 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.
> 
> Yeah, zone span should exclude those pages, but you still somehow handle them?
> That's how I read "pages that are not spanned by any node will get links to the
> adjacent zone/node."
> So is it always a unique zone/node can be determined?
> 
> Let's say we have:
> 
> <memory on node 0>
> ---- pageblock boundary ----
> <more memory on node 0>
> <a hole>
> <memory on node 1>
> ---- pageblock boundary ----
> 
> Now I hope such configurations don't really exist :) But if we simulated them in
> QEMU, what would be the linkage in struct pages in that hole?

I don't think such configuration is possible in practice but it can be
forced with e.g memmap="2M hole at 4G - 1M".

The hole in your example the hole will get node1 for node and zone that
spans the beginning of node1 for zone.
 
-- 
Sincerely yours,
Mike.

Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

[Vlastimil Babka]

On 2/26/21 11:59 AM, Mike Rapoport wrote:
> On Thu, Feb 25, 2021 at 07:38:44PM +0100, Vlastimil Babka wrote:
>> On 2/25/21 7:05 PM, Mike Rapoport wrote:
>> >> 
>> >> 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.
>> 
>> Yeah, zone span should exclude those pages, but you still somehow handle them?
>> That's how I read "pages that are not spanned by any node will get links to the
>> adjacent zone/node."
>> So is it always a unique zone/node can be determined?
>> 
>> Let's say we have:
>> 
>> <memory on node 0>
>> ---- pageblock boundary ----
>> <more memory on node 0>
>> <a hole>
>> <memory on node 1>
>> ---- pageblock boundary ----
>> 
>> Now I hope such configurations don't really exist :) But if we simulated them in
>> QEMU, what would be the linkage in struct pages in that hole?
> 
> I don't think such configuration is possible in practice but it can be
> forced with e.g memmap="2M hole at 4G - 1M".

Right.

> The hole in your example the hole will get node1 for node and zone that
> spans the beginning of node1 for zone.

Yeah the comments in v8 make that clear now, thanks!