mm/memblock: introduce a new helper memblock_estimated_nr_free_pages()

During bootup, system may need the number of free pages in the whole system
to do some calculation before all pages are freed to buddy system. Usually
this number is get from totalram_pages(). Since we plan to move the free
pages accounting in __free_pages_core(), this value may not represent
total free pages at the early stage, especially when
CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.

Instead of using raw memblock api, let's introduce a new helper for user
to get the estimated number of free pages from memblock point of view.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20240808001415.6298-1-richard.weiyang@gmail.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index fc4d75c6cec3eb5a4b5530ba8c1d8298c225640c..673d5cae7c8134031cfc9a85b8aff8bc209d4d3d 100644 (file)
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -467,6 +467,7 @@ static inline __init_memblock bool memblock_bottom_up(void)
 
 phys_addr_t memblock_phys_mem_size(void);
 phys_addr_t memblock_reserved_size(void);
+unsigned long memblock_estimated_nr_free_pages(void);
 phys_addr_t memblock_start_of_DRAM(void);
 phys_addr_t memblock_end_of_DRAM(void);
 void memblock_enforce_memory_limit(phys_addr_t memory_limit);

diff --git a/mm/memblock.c b/mm/memblock.c
index 3b9dc2d89b8a08aec17444e735ab3ef8d6fc07d7..213057603b650612baf7bc352f0c54ea50006e07 100644 (file)
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1731,6 +1731,23 @@ phys_addr_t __init_memblock memblock_reserved_size(void)
        return memblock.reserved.total_size;
 }
 
+/**
+ * memblock_estimated_nr_free_pages - return estimated number of free pages
+ * from memblock point of view
+ *
+ * During bootup, subsystems might need a rough estimate of the number of free
+ * pages in the whole system, before precise numbers are available from the
+ * buddy. Especially with CONFIG_DEFERRED_STRUCT_PAGE_INIT, the numbers
+ * obtained from the buddy might be very imprecise during bootup.
+ *
+ * Return:
+ * An estimated number of free pages from memblock point of view.
+ */
+unsigned long __init memblock_estimated_nr_free_pages(void)
+{
+       return PHYS_PFN(memblock_phys_mem_size() - memblock_reserved_size());
+}
+
 /* lowest address */
 phys_addr_t __init_memblock memblock_start_of_DRAM(void)
 {

diff --git a/tools/include/linux/pfn.h b/tools/include/linux/pfn.h
index 7512a58189ebd13d5b4f56f0b1356f585a07306a..f77a30d701527e334cb48eac38785c7ae63a833a 100644 (file)
--- a/tools/include/linux/pfn.h
+++ b/tools/include/linux/pfn.h
@@ -7,4 +7,5 @@
 #define PFN_UP(x)      (((x) + PAGE_SIZE - 1) >> PAGE_SHIFT)
 #define PFN_DOWN(x)    ((x) >> PAGE_SHIFT)
 #define PFN_PHYS(x)    ((phys_addr_t)(x) << PAGE_SHIFT)
+#define PHYS_PFN(x)    ((unsigned long)((x) >> PAGE_SHIFT))
 #endif