[6/6] sparsemem hotplug base

Andy Whitcroft
2005-05-04T20:36:39Z

Make sparse's initalization be accessible at runtime. This
allows sparse mappings to be created after boot in a hotplug
situation.

This patch is separated from the previous one just to give an
indication how much of the sparse infrastructure is *just* for
hotplug memory.

The section_mem_map doesn't really store a pointer. It stores
something that is convenient to do some math against to get a
pointer. It isn't valid to just do *section_mem_map, so I
don't think it should be stored as a pointer.

There are a couple of things I'd like to store about a section.
First of all, the fact that it is !NULL does not mean that it
is present. There could be such a combination where
section_mem_map *is* NULL, but the math gets you properly to
a real mem_map. So, I don't think that check is safe.

Since we're storing 32-bit-aligned structures, we have a few
bits in the bottom of the pointer to play with. Use one bit
to encode whether there's really a mem_map there, and the
other one to tell whether there's a valid section there. We
need to distinguish between the two because sometimes there's
a gap between when a section is discovered to be present and
when we can get the mem_map for it.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
---
include/linux/mmzone.h | 48 +++++++++++++++++++++++--
mm/sparse.c | 92 ++++++++++++++++++++++++++++++++++++++-----------
2 files changed, 116 insertions(+), 24 deletions(-)

diff -X /home/apw/brief/lib/vdiff.excl -rupN reference/include/linux/mmzone.h current/include/linux/mmzone.h
--- reference/include/linux/mmzone.h 2005-05-04 20:54:41.000000000 +0100
+++ current/include/linux/mmzone.h 2005-05-04 20:54:43.000000000 +0100
@@ -459,12 +459,52 @@ extern struct pglist_data contig_page_da

struct page;
struct mem_section {
- struct page *section_mem_map;
+ /*
+ * This is, logically, a pointer to an array of struct
+ * pages. However, it is stored with some other magic.
+ * (see sparse.c::sparse_init_one_section())
+ *
+ * Making it a UL at least makes someone do a cast
+ * before using it wrong.
+ */
+ unsigned long section_mem_map;
};

extern struct mem_section mem_section[NR_MEM_SECTIONS];

/*
+ * We use the lower bits of the mem_map pointer to store
+ * a little bit of information. There should be at least
+ * 3 bits here due to 32-bit alignment.
+ */
+#define SECTION_MARKED_PRESENT (1UL<<0)
+#define SECTION_HAS_MEM_MAP (1UL<<1)
+#define SECTION_MAP_LAST_BIT (1UL<<2)
+#define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1))
+
+static inline struct page *__section_mem_map_addr(struct mem_section *section)
+{
+ unsigned long map = section->section_mem_map;
+ map &= SECTION_MAP_MASK;
+ return (struct page *)map;
+}
+
+static inline int valid_section(struct mem_section *section)
+{
+ return (section->section_mem_map & SECTION_MARKED_PRESENT);
+}
+
+static inline int section_has_mem_map(struct mem_section *section)
+{
+ return (section->section_mem_map & SECTION_HAS_MEM_MAP);
+}
+
+static inline int valid_section_nr(int nr)
+{
+ return valid_section(&mem_section[nr]);
+}
+
+/*
* Given a kernel address, find the home node of the underlying memory.
*/
#define kvaddr_to_nid(kaddr) pfn_to_nid(__pa(kaddr) >> PAGE_SHIFT)
@@ -477,18 +517,18 @@ static inline struct mem_section *__pfn_
#define pfn_to_page(pfn) \
({ \
unsigned long __pfn = (pfn); \
- __pfn_to_section(__pfn)->section_mem_map + __pfn; \
+ __section_mem_map_addr(__pfn_to_section(__pfn)) + __pfn; \
})
#define page_to_pfn(page) \
({ \
- page - mem_section[page_to_section(page)].section_mem_map; \
+ page - __section_mem_map_addr(&mem_section[page_to_section(page)]); \
})

static inline int pfn_valid(unsigned long pfn)
{
if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
return 0;
- return mem_section[pfn_to_section_nr(pfn)].section_mem_map != 0;
+ return valid_section(&mem_section[pfn_to_section_nr(pfn)]);
}

/*
diff -X /home/apw/brief/lib/vdiff.excl -rupN reference/mm/sparse.c current/mm/sparse.c
--- reference/mm/sparse.c 2005-05-04 20:54:33.000000000 +0100
+++ current/mm/sparse.c 2005-05-04 20:54:44.000000000 +0100
@@ -25,7 +25,7 @@ void memory_present(int nid, unsigned lo
for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
unsigned long section = pfn_to_section_nr(pfn);
if (!mem_section[section].section_mem_map)
- mem_section[section].section_mem_map = (void *) -1;
+ mem_section[section].section_mem_map = SECTION_MARKED_PRESENT;
}
}

@@ -51,6 +51,56 @@ unsigned long __init node_memmap_size_by
}

/*
+ * Subtle, we encode the real pfn into the mem_map such that
+ * the identity pfn - section_mem_map will return the actual
+ * physical page frame number.
+ */
+static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long pnum)
+{
+ return (unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
+}
+
+/*
+ * We need this if we ever free the mem_maps. While not implemented yet,
+ * this function is included for parity with its sibling.
+ */
+static __attribute((unused))
+struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pnum)
+{
+ return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum);
+}
+
+static int sparse_init_one_section(struct mem_section *ms,
+ unsigned long pnum, struct page *mem_map)
+{
+ if (!valid_section(ms))
+ return -EINVAL;
+
+ ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum);
+
+ return 1;
+}
+
+static struct page *sparse_early_mem_map_alloc(unsigned long pnum)
+{
+ struct page *map;
+ int nid = early_pfn_to_nid(section_nr_to_pfn(pnum));
+
+ map = alloc_remap(nid, sizeof(struct page) * PAGES_PER_SECTION);
+ if (map)
+ return map;
+
+ map = alloc_bootmem_node(NODE_DATA(nid),
+ sizeof(struct page) * PAGES_PER_SECTION);
+ if (map)
+ return map;
+
+ printk(KERN_WARNING "%s: allocation failed\n", __FUNCTION__);
+ mem_section[pnum].section_mem_map = 0;
+ return NULL;
+}
+
+/*
* Allocate the accumulated non-linear sections, allocate a mem_map
* for each and record the physical to section mapping.
*/
@@ -58,28 +108,30 @@ void sparse_init(void)
{
unsigned long pnum;
struct page *map;
- int nid;

for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
- if (!mem_section[pnum].section_mem_map)
- continue;
-
- nid = early_pfn_to_nid(section_nr_to_pfn(pnum));
- map = alloc_remap(nid, sizeof(struct page) * PAGES_PER_SECTION);
- if (!map)
- map = alloc_bootmem_node(NODE_DATA(nid),
- sizeof(struct page) * PAGES_PER_SECTION);
- if (!map) {
- mem_section[pnum].section_mem_map = 0;
+ if (!valid_section_nr(pnum))
continue;
- }

- /*
- * Subtle, we encode the real pfn into the mem_map such that
- * the identity pfn - section_mem_map will return the actual
- * physical page frame number.
- */
- mem_section[pnum].section_mem_map = map -
- section_nr_to_pfn(pnum);
+ map = sparse_early_mem_map_alloc(pnum);
+ if (map)
+ sparse_init_one_section(&mem_section[pnum], pnum, map);
}
}
+
+/*
+ * returns the number of sections whose mem_maps were properly
+ * set. If this is <=0, then that means that the passed-in
+ * map was not consumed and must be freed.
+ */
+int sparse_add_one_section(int start_pfn, int nr_pages, struct page *map)
+{
+ struct mem_section *ms = __pfn_to_section(start_pfn);
+
+ if (ms->section_mem_map & SECTION_MARKED_PRESENT)
+ return -EEXIST;
+
+ ms->section_mem_map |= SECTION_MARKED_PRESENT;
+
+ return sparse_init_one_section(ms, pfn_to_section_nr(start_pfn), map);
+}