memblock: introduce MEMBLOCK_RSRV_NOINIT flag

For reserved memory regions marked with this flag, reserve_bootmem_region
is not called during memmap_init_reserved_pages.  This can be used to
avoid struct page initialization for regions which won't need them, for
e.g.  hugepages with Hugepage Vmemmap Optimization enabled.

Link: https://lkml.kernel.org/r/20230913105401.519709-4-usama.arif@bytedance.com
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Acked-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 1c1072e3ca063544c93288bcf3dbba15aa6f2616..ae3bde302f704ad1c464efc4e3f6cf09f164c5d3 100644 (file)
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -40,6 +40,8 @@ extern unsigned long long max_possible_pfn;
  * via a driver, and never indicated in the firmware-provided memory map as
  * system RAM. This corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED in the
  * kernel resource tree.
+ * @MEMBLOCK_RSRV_NOINIT: memory region for which struct pages are
+ * not initialized (only for reserved regions).
  */
 enum memblock_flags {
        MEMBLOCK_NONE           = 0x0,  /* No special request */
@@ -47,6 +49,7 @@ enum memblock_flags {
        MEMBLOCK_MIRROR         = 0x2,  /* mirrored region */
        MEMBLOCK_NOMAP          = 0x4,  /* don't add to kernel direct mapping */
        MEMBLOCK_DRIVER_MANAGED = 0x8,  /* always detected via a driver */
+       MEMBLOCK_RSRV_NOINIT    = 0x10, /* don't initialize struct pages */
 };
 
 /**
@@ -125,6 +128,7 @@ int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
 int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
 int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
+int memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size);
 
 void memblock_free_all(void);
 void memblock_free(void *ptr, size_t size);
@@ -259,6 +263,11 @@ static inline bool memblock_is_nomap(struct memblock_region *m)
        return m->flags & MEMBLOCK_NOMAP;
 }
 
+static inline bool memblock_is_reserved_noinit(struct memblock_region *m)
+{
+       return m->flags & MEMBLOCK_RSRV_NOINIT;
+}
+
 static inline bool memblock_is_driver_managed(struct memblock_region *m)
 {
        return m->flags & MEMBLOCK_DRIVER_MANAGED;

diff --git a/mm/memblock.c b/mm/memblock.c
index b978cda96cf08818438d79443d58089e6646f358..fd492e5bbdbcde42497a513fded38048bce91bde 100644 (file)
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -997,6 +997,24 @@ int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
        return memblock_setclr_flag(&memblock.memory, base, size, 0, MEMBLOCK_NOMAP);
 }
 
+/**
+ * memblock_reserved_mark_noinit - Mark a reserved memory region with flag
+ * MEMBLOCK_RSRV_NOINIT which results in the struct pages not being initialized
+ * for this region.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * struct pages will not be initialized for reserved memory regions marked with
+ * %MEMBLOCK_RSRV_NOINIT.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size)
+{
+       return memblock_setclr_flag(&memblock.reserved, base, size, 1,
+                                   MEMBLOCK_RSRV_NOINIT);
+}
+
 static bool should_skip_region(struct memblock_type *type,
                               struct memblock_region *m,
                               int nid, int flags)
@@ -2113,13 +2131,18 @@ static void __init memmap_init_reserved_pages(void)
                memblock_set_node(start, end, &memblock.reserved, nid);
        }
 
-       /* initialize struct pages for the reserved regions */
+       /*
+        * initialize struct pages for reserved regions that don't have
+        * the MEMBLOCK_RSRV_NOINIT flag set
+        */
        for_each_reserved_mem_region(region) {
-               nid = memblock_get_region_node(region);
-               start = region->base;
-               end = start + region->size;
+               if (!memblock_is_reserved_noinit(region)) {
+                       nid = memblock_get_region_node(region);
+                       start = region->base;
+                       end = start + region->size;
 
-               reserve_bootmem_region(start, end, nid);
+                       reserve_bootmem_region(start, end, nid);
+               }
        }
 }