[PATCH v4 3/6] powerpc/vmemmap: Add altmap support

[Oliver O'Halloran]

Adds support to powerpc for the altmap feature of ZONE_DEVICE memory. An
altmap is a driver provided region that is used to provide the backing
storage for the struct pages of ZONE_DEVICE memory. In situations where
large amount of ZONE_DEVICE memory is being added to the system the
altmap reduces pressure on main system memory by allowing the mm/
metadata to be stored on the device itself rather in main memory.

Reviewed-by: Balbir Singh <bsinghar...@gmail.com>
Signed-off-by: Oliver O'Halloran <ooh...@gmail.com>
---
 arch/powerpc/mm/init_64.c | 15 +++++++++++++--
 arch/powerpc/mm/mem.c     | 16 +++++++++++++---
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 8851e4f5dbab..225fbb8034e6 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -44,6 +44,7 @@
 #include <linux/slab.h>
 #include <linux/of_fdt.h>
 #include <linux/libfdt.h>
+#include <linux/memremap.h>
 
 #include <asm/pgalloc.h>
 #include <asm/page.h>
@@ -171,13 +172,17 @@ int __meminit vmemmap_populate(unsigned long start, 
unsigned long end, int node)
        pr_debug("vmemmap_populate %lx..%lx, node %d\n", start, end, node);
 
        for (; start < end; start += page_size) {
+               struct vmem_altmap *altmap;
                void *p;
                int rc;
 
                if (vmemmap_populated(start, page_size))
                        continue;
 
-               p = vmemmap_alloc_block(page_size, node);
+               /* altmap lookups only work at section boundaries */
+               altmap = to_vmem_altmap(SECTION_ALIGN_DOWN(start));
+
+               p =  __vmemmap_alloc_block_buf(page_size, node, altmap);
                if (!p)
                        return -ENOMEM;
 
@@ -242,6 +247,8 @@ void __ref vmemmap_free(unsigned long start, unsigned long 
end)
 
        for (; start < end; start += page_size) {
                unsigned long nr_pages, addr;
+               struct vmem_altmap *altmap;
+               struct page *section_base;
                struct page *page;
 
                /*
@@ -257,9 +264,13 @@ void __ref vmemmap_free(unsigned long start, unsigned long 
end)
                        continue;
 
                page = pfn_to_page(addr >> PAGE_SHIFT);
+               section_base = pfn_to_page(vmemmap_section_start(start));
                nr_pages = 1 << page_order;
 
-               if (PageReserved(page)) {
+               altmap = to_vmem_altmap((unsigned long) section_base);
+               if (altmap) {
+                       vmem_altmap_free(altmap, nr_pages);
+               } else if (PageReserved(page)) {
                        /* allocated from bootmem */
                        if (page_size < PAGE_SIZE) {
                                /*
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 8e9bef964dbf..8541f18694a4 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -36,6 +36,7 @@
 #include <linux/hugetlb.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
+#include <linux/memremap.h>
 
 #include <asm/pgalloc.h>
 #include <asm/prom.h>
@@ -151,11 +152,20 @@ int arch_remove_memory(u64 start, u64 size)
 {
        unsigned long start_pfn = start >> PAGE_SHIFT;
        unsigned long nr_pages = size >> PAGE_SHIFT;
-       struct zone *zone;
+       struct vmem_altmap *altmap;
+       struct page *page;
        int ret;
 
-       zone = page_zone(pfn_to_page(start_pfn));
-       ret = __remove_pages(zone, start_pfn, nr_pages);
+       /*
+        * If we have an altmap then we need to skip over any reserved PFNs
+        * when querying the zone.
+        */
+       page = pfn_to_page(start_pfn);
+       altmap = to_vmem_altmap((unsigned long) page);
+       if (altmap)
+               page += vmem_altmap_offset(altmap);
+
+       ret = __remove_pages(page_zone(page), start_pfn, nr_pages);
        if (ret)
                return ret;
 
-- 
2.9.4