[PATCH 3/4] mm: Set page count and mark page reserved in reserve_bootmem_region

Yajun Deng
2023-09-22T07:10:28Z

memmap_init_range() would set page count of all pages, but the free
pages count would be reset in __free_pages_core(). These two are
opposite operations. It's unnecessary and time-consuming when it's
in MEMINIT_EARLY context.

Set page count and mark page reserved in reserve_bootmem_region when
in MEMINIT_EARLY context, and change the context from MEMINIT_LATE
to MEMINIT_EARLY in __free_pages_memory.

At the same time, the init list head in reserve_bootmem_region isn't
need. As it already done in __init_single_page.

The following data was tested on an x86 machine with 190GB of RAM.

before:
free_low_memory_core_early() 342ms

after:
free_low_memory_core_early() 286ms

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
mm/memblock.c | 2 +-
mm/mm_init.c | 20 ++++++++++++++------
mm/page_alloc.c | 8 +++++---
3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index a32364366bb2..9276f1819982 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2089,7 +2089,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
while (start + (1UL << order) > end)
order--;

- memblock_free_pages(start, order, MEMINIT_LATE);
+ memblock_free_pages(start, order, MEMINIT_EARLY);

start += (1UL << order);
}
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 0a4437aae30d..1cc310f706a9 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -718,7 +718,7 @@ static void __meminit init_reserved_page(unsigned long pfn, int nid)
if (zone_spans_pfn(zone, pfn))
break;
}
- __init_single_page(pfn_to_page(pfn), pfn, zid, nid, true, false);
+ __init_single_page(pfn_to_page(pfn), pfn, zid, nid, false, false);
}
#else
static inline void pgdat_set_deferred_range(pg_data_t *pgdat) {}
@@ -756,8 +756,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start,

init_reserved_page(start_pfn, nid);

- /* Avoid false-positive PageTail() */
- INIT_LIST_HEAD(&page->lru);
+ /* Set page count for the reserve region */
+ init_page_count(page);

/*
* no need for atomic set_bit because the struct
@@ -888,9 +888,17 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
}

page = pfn_to_page(pfn);
- __init_single_page(page, pfn, zone, nid, true, false);
- if (context == MEMINIT_HOTPLUG)
- __SetPageReserved(page);
+
+ /* If the context is MEMINIT_EARLY, we will set page count and
+ * mark page reserved in reserve_bootmem_region, the free region
+ * wouldn't have page count and reserved flag and we don't
+ * need to reset pages count and clear reserved flag in
+ * __free_pages_core.
+ */
+ if (context == MEMINIT_EARLY)
+ __init_single_page(page, pfn, zone, nid, false, false);
+ else
+ __init_single_page(page, pfn, zone, nid, true, true);

/*
* Usually, we want to mark the pageblock MIGRATE_MOVABLE,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6c4f4531bee0..6ac58c5f3b00 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1285,9 +1285,11 @@ void __free_pages_core(struct page *page, unsigned int order, enum meminit_conte
unsigned int loop;

/*
- * When initializing the memmap, __init_single_page() sets the refcount
- * of all pages to 1 ("allocated"/"not free"). We have to set the
- * refcount of all involved pages to 0.
+ * When initializing the memmap, memmap_init_range sets the refcount
+ * of all pages to 1 ("allocated"/"not free") in hotplug context. We
+ * have to set the refcount of all involved pages to 0. Otherwise,
+ * we don't do it, as reserve_bootmem_region only set the refcount on
+ * reserve region ("allocated") in early context.
*/
if (context != MEMINIT_EARLY) {
prefetchw(p);
--
2.25.1