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Message-ID: <a684b0e8-4412-79c8-2926-7822b1163c15@bytedance.com>
Date: Fri, 28 Jul 2023 14:47:08 +0100
From: Usama Arif <usama.arif@...edance.com>
To: Mika Penttilä <mpenttil@...hat.com>,
linux-mm@...ck.org, muchun.song@...ux.dev, mike.kravetz@...cle.com,
rppt@...nel.org
Cc: linux-kernel@...r.kernel.org, fam.zheng@...edance.com,
liangma@...ngbit.com, simon.evans@...edance.com,
punit.agrawal@...edance.com
Subject: Re: [External] Re: [v1 4/6] memblock: introduce MEMBLOCK_RSRV_NOINIT
flag
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@...edance.com>
>> ---
>> 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.
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
>
>
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