Some memory is reserved but unavailable: not present in memblock.memory
(because not backed by physical pages), but present in memblock.reserved.
Such memory has backing struct pages, but they are not initialized by going
through __init_single_page().
In some cases these struct pages are accessed even if they do not contain
any data. One example is page_to_pfn() might access page->flags if this is
where section information is stored (CONFIG_SPARSEMEM,
SECTION_IN_PAGE_FLAGS).
One example of such memory: trim_low_memory_range() unconditionally
reserves from pfn 0, but e820__memblock_setup() might provide the exiting
memory from pfn 1 (i.e. KVM).
Since, struct pages are zeroed in __init_single_page(), and not during
allocation time, we must zero such struct pages explicitly.
The patch involves adding a new memblock iterator:
for_each_resv_unavail_range(i, p_start, p_end)
Which iterates through reserved && !memory lists, and we zero struct pages
explicitly by calling mm_zero_struct_page().
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx>
---
include/linux/memblock.h | 16 ++++++++++++++++
include/linux/mm.h | 15 +++++++++++++++
mm/page_alloc.c | 38 ++++++++++++++++++++++++++++++++++++++
3 files changed, 69 insertions(+)
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index bae11c7e7bf3..ce8bfa5f3e9b 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -237,6 +237,22 @@ unsigned long memblock_next_valid_pfn(unsigned long pfn, unsigned long max_pfn);
for_each_mem_range_rev(i, &memblock.memory, &memblock.reserved, \
nid, flags, p_start, p_end, p_nid)
+/**
+ * for_each_resv_unavail_range - iterate through reserved and unavailable memory
+ * @i: u64 used as loop variable
+ * @flags: pick from blocks based on memory attributes
+ * @p_start: ptr to phys_addr_t for start address of the range, can be %NULL
+ * @p_end: ptr to phys_addr_t for end address of the range, can be %NULL
+ *
+ * Walks over unavailable but reserved (reserved && !memory) areas of memblock.
+ * Available as soon as memblock is initialized.
+ * Note: because this memory does not belong to any physical node, flags and
+ * nid arguments do not make sense and thus not exported as arguments.
+ */
+#define for_each_resv_unavail_range(i, p_start, p_end) \
+ for_each_mem_range(i, &memblock.reserved, &memblock.memory, \
+ NUMA_NO_NODE, MEMBLOCK_NONE, p_start, p_end, NULL)
+
static inline void memblock_set_region_flags(struct memblock_region *r,
unsigned long flags)
{
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 065d99deb847..04c8b2e5aff4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -94,6 +94,15 @@ extern int mmap_rnd_compat_bits __read_mostly;
#define mm_forbids_zeropage(X) (0)
#endif
+/*
+ * On some architectures it is expensive to call memset() for small sizes.
+ * Those architectures should provide their own implementation of "struct page"
+ * zeroing by defining this macro in <asm/pgtable.h>.
+ */
+#ifndef mm_zero_struct_page
+#define mm_zero_struct_page(pp) ((void)memset((pp), 0, sizeof(struct page)))
+#endif
+
/*
* Default maximum number of active map areas, this limits the number of vmas
* per mm struct. Users can overwrite this number by sysctl but there is a
@@ -2001,6 +2010,12 @@ extern int __meminit __early_pfn_to_nid(unsigned long pfn,
struct mminit_pfnnid_cache *state);
#endif
+#ifdef CONFIG_HAVE_MEMBLOCK
+void zero_resv_unavail(void);
+#else
+static inline void zero_resv_unavail(void) {}
+#endif
+
extern void set_dma_reserve(unsigned long new_dma_reserve);
extern void memmap_init_zone(unsigned long, int, unsigned long,
unsigned long, enum memmap_context);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 20b0bace2235..5f0013bbbe9d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6209,6 +6209,42 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
free_area_init_core(pgdat);
}
+#ifdef CONFIG_HAVE_MEMBLOCK
+/*
+ * 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 zero those struct pages.
+ */
+void __paginginit zero_resv_unavail(void)
+{
+ phys_addr_t start, end;
+ unsigned long pfn;
+ u64 i, pgcnt;
+
+ /* Loop through ranges that are reserved, but do not have reported
+ * physical memory backing.
+ */
+ pgcnt = 0;
+ for_each_resv_unavail_range(i, &start, &end) {
+ for (pfn = PFN_DOWN(start); pfn < PFN_UP(end); pfn++) {
+ mm_zero_struct_page(pfn_to_page(pfn));
+ pgcnt++;
+ }
+ }
+
+ /*
+ * Struct pages that do not have backing memory. This could be because
+ * firmware is using some of this memory, or for some other reasons.
+ * Once memblock is changed so such behaviour is not allowed: i.e.
+ * list of "reserved" memory must be a subset of list of "memory", then
+ * this code can be removed.
+ */
+ pr_info("Reserved but unavailable: %lld pages", pgcnt);
+}
+#endif /* CONFIG_HAVE_MEMBLOCK */
+
#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
#if MAX_NUMNODES > 1
@@ -6632,6 +6668,7 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn)
node_set_state(nid, N_MEMORY);
check_for_memory(pgdat, nid);
}
+ zero_resv_unavail();
}
static int __init cmdline_parse_core(char *p, unsigned long *core)
@@ -6795,6 +6832,7 @@ void __init free_area_init(unsigned long *zones_size)
{
free_area_init_node(0, zones_size,
__pa(PAGE_OFFSET) >> PAGE_SHIFT, NULL);
+ zero_resv_unavail();
}
static int page_alloc_cpu_dead(unsigned int cpu)
--
2.14.2
--
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