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Date: Fri, 28 Jul 2023 18:51:32 +0300
From: Mika Penttilä <mpenttil@...hat.com>
To: Usama Arif <usama.arif@...edance.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 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@...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.
>
>
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
>>
>>
>
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