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Subject[PATCH 2/4] mm: Create non-atomic version of SetPageReserved for init use
From: Alexander Duyck <>

It doesn't make much sense to use the atomic SetPageReserved at init time
when we are using memset to clear the memory and manipulating the page
flags via simple "&=" and "|=" operations in __init_single_page.

This patch adds a non-atomic version __SetPageReserved that can be used
during page init and shows about a 10% improvement in initialization times
on the systems I have available for testing. On those systems I saw
initialization times drop from around 35 seconds to around 32 seconds to
initialize a 3TB block of persistent memory.

I tried adding a bit of documentation based on commit <f1dd2cd13c4> ("mm,
memory_hotplug: do not associate hotadded memory to zones until online").

Ideally the reserved flag should be set earlier since there is a brief
window where the page is initialization via __init_single_page and we have
not set the PG_Reserved flag. I'm leaving that for a future patch set as
that will require a more significant refactor.

Acked-by: Michal Hocko <>
Signed-off-by: Alexander Duyck <>
include/linux/page-flags.h | 1 +
mm/page_alloc.c | 17 +++++++++++++++--
2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d00216cf00f8..1b1f8e0378ae 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -300,6 +300,7 @@ static inline void page_init_poison(struct page *page, size_t size)

PAGEFLAG(Reserved, reserved, PF_NO_COMPOUND)
+ __SETPAGEFLAG(Reserved, reserved, PF_NO_COMPOUND)
PAGEFLAG(SwapBacked, swapbacked, PF_NO_TAIL)
__CLEARPAGEFLAG(SwapBacked, swapbacked, PF_NO_TAIL)
__SETPAGEFLAG(SwapBacked, swapbacked, PF_NO_TAIL)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 89d2a2ab3fe6..a9b095a72fd9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1231,7 +1231,12 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
/* Avoid false-positive PageTail() */

- SetPageReserved(page);
+ /*
+ * no need for atomic set_bit because the struct
+ * page is not visible yet so nobody should
+ * access it yet.
+ */
+ __SetPageReserved(page);
@@ -5517,8 +5522,16 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
page = pfn_to_page(pfn);
__init_single_page(page, pfn, zone, nid);
+ /*
+ * Mark page reserved as it will need to wait for onlining
+ * phase for it to be fully associated with a zone.
+ *
+ * We can use the non-atomic __set_bit operation for setting
+ * the flag as we are still initializing the pages.
+ */
if (context == MEMMAP_HOTPLUG)
- SetPageReserved(page);
+ __SetPageReserved(page);

* Mark the block movable so that blocks are reserved for
 \ /
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