Re: [External] Re: [v1 4/6] memblock: introduce MEMBLOCK_RSRV_NOINIT flag
From: Mika Penttilä
Date: Fri Jul 28 2023 - 11:52:48 EST
On 7/28/23 16:47, Usama Arif wrote:
On 28/07/2023 05:30, Mika Penttilä wrote:
Hi,
On 7/27/23 23:46, Usama Arif wrote:
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
HVO enabled.
Signed-off-by: Usama Arif <usama.arif@xxxxxxxxxxxxx>
---
include/linux/memblock.h | 7 +++++++
mm/memblock.c | 32 ++++++++++++++++++++++++++------
2 files changed, 33 insertions(+), 6 deletions(-)
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index f71ff9f0ec81..7f9d06c08592 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -47,6 +47,7 @@ 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 call
reserve_bootmem_region for this region */
};
/**
@@ -125,6 +126,7 @@ 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_rsrv_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 +261,11 @@ static inline bool memblock_is_nomap(struct
memblock_region *m)
return m->flags & MEMBLOCK_NOMAP;
}
+static inline bool memblock_is_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 4fd431d16ef2..3a15708af3b6 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -997,6 +997,22 @@ int __init_memblock
memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
return memblock_setclr_flag(base, size, 0, MEMBLOCK_NOMAP, 0);
}
+/**
+ * memblock_rsrv_mark_noinit - Mark a reserved memory region with
flag MEMBLOCK_RSRV_NOINIT.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * For memory regions marked with %MEMBLOCK_RSRV_NOINIT,
reserve_bootmem_region
+ * is not called during memmap_init_reserved_pages, hence struct
pages are not
+ * initialized for this region.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_rsrv_mark_noinit(phys_addr_t base,
phys_addr_t size)
+{
+ return memblock_setclr_flag(base, size, 1,
MEMBLOCK_RSRV_NOINIT, 1);
+}
+
static bool should_skip_region(struct memblock_type *type,
struct memblock_region *m,
int nid, int flags)
@@ -2113,13 +2129,17 @@ 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;
-
- reserve_bootmem_region(start, end, nid);
+ if (!memblock_is_noinit(region)) {
+ nid = memblock_get_region_node(region);
+ start = region->base;
+ end = start + region->size;
+ reserve_bootmem_region(start, end, nid);
+ }
}
}
There's code like:
static inline void free_vmemmap_page(struct page *page)
{
if (PageReserved(page))
free_bootmem_page(page);
else
__free_page(page);
}
which depends on the PageReserved being in vmempages pages, so I
think you can't skip that part?
free_vmemmap_page_list (free_vmemmap_page) is called on struct pages
(refer to as [1]) that point to memory *which contains* the struct
pages (refer to as [2]) for the hugepage. The above if
(!memblock_is_noinit(region)) to not reserve_bootmem_region is called
for the struct pages [2] for the hugepage. struct pages [1] are not
changed with my patch.
As an experiment if I run the diff at the bottom with and without
these patches I get the same log "HugeTLB: reserved pages 4096, normal
pages 0", which means those struct pages are treated the same without
and without these patches. (Its 4096 as 262144 struct pages [2] per
hugepage * 64 bytes per struct page / PAGE_SIZE = 4096 struct pages [1] )
Also should have mentioned in cover letter, I used cat /proc/meminfo
to make sure it was working as expected. Reserving 500 1G hugepages
with and without these patches when hugetlb_free_vmemmap=on
MemTotal: 536207112 kB (511.4G)
when hugetlb_free_vmemmap=off
MemTotal: 528015112 kB (503G)
The expectation is that for 500 1G hugepages, when using HVO we have a
saving of 16380K*500=~8GB which is what we see with and without those
patches (511.4G - 503G). These patches didnt affect these numbers.
You are right, thanks for the explanation!
--Mika
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index b5b7834e0f42..bc0ec90552b7 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -208,6 +208,8 @@ static int vmemmap_remap_range(unsigned long
start, unsigned long end,
return 0;
}
+static int i = 0, j = 0;
+
/*
* Free a vmemmap page. A vmemmap page can be allocated from the
memblock
* allocator or buddy allocator. If the PG_reserved flag is set, it
means
@@ -216,10 +218,14 @@ static int vmemmap_remap_range(unsigned long
start, unsigned long end,
*/
static inline void free_vmemmap_page(struct page *page)
{
- if (PageReserved(page))
+ if (PageReserved(page)) {
+ i++;
free_bootmem_page(page);
- else
+ }
+ else {
+ j++;
__free_page(page);
+ }
}
/* Free a list of the vmemmap pages */
@@ -380,6 +386,7 @@ static int vmemmap_remap_free(unsigned long start,
unsigned long end,
free_vmemmap_page_list(&vmemmap_pages);
+ pr_err("reserved pages %u, normal pages %u", i, j);
return ret;
}
--Mika