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Message-ID: <2be1ab83-f047-245f-68ad-62c4478914a5@linux.dev>
Date: Mon, 28 Aug 2023 16:52:10 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Mike Rapoport <rppt@...nel.org>,
Usama Arif <usama.arif@...edance.com>
Cc: linux-mm@...ck.org, mike.kravetz@...cle.com,
linux-kernel@...r.kernel.org, songmuchun@...edance.com,
fam.zheng@...edance.com, liangma@...ngbit.com,
punit.agrawal@...edance.com
Subject: Re: [v3 3/4] memblock: introduce MEMBLOCK_RSRV_NOINIT_VMEMMAP flag
On 2023/8/28 15:47, Mike Rapoport wrote:
> On Fri, Aug 25, 2023 at 12:18:35PM +0100, 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 | 10 ++++++++++
>> mm/memblock.c | 32 +++++++++++++++++++++++++++-----
>> 2 files changed, 37 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> index f71ff9f0ec81..6d681d053880 100644
>> --- a/include/linux/memblock.h
>> +++ b/include/linux/memblock.h
>> @@ -40,6 +40,8 @@ extern unsigned long long max_possible_pfn;
>> * via a driver, and never indicated in the firmware-provided memory map as
>> * system RAM. This corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED in the
>> * kernel resource tree.
>> + * @MEMBLOCK_RSRV_NOINIT_VMEMMAP: memory region for which struct pages are
>> + * not initialized (only for reserved regions).
>> */
>> enum memblock_flags {
>> MEMBLOCK_NONE = 0x0, /* No special request */
>> @@ -47,6 +49,8 @@ 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 */
>> + /* don't initialize struct pages associated with this reserver memory block */
>> + MEMBLOCK_RSRV_NOINIT_VMEMMAP = 0x10,
> The flag means that struct page shouldn't be initialized, it may be used
> not only by vmemmap optimizations.
> Please drop _VMEMMAP.
The area at where the struct pages located is vmemmap, I think the
"vmemap" suffix does not mean that it is for "vmemmap optimization",
it could specify the target which will not be initialized. For me,
MEMBLOCK_RSRV_NOINIT does not tell me what should not be initialized,
memblock itself or its struct page (aka vmemmap pages)? So maybe
the suffix is better to keep?
>
> And I agree with Muchun's remarks about the comments.
>
>
>
>> };
>>
>> /**
>> @@ -125,6 +129,7 @@ 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_reserved_mark_noinit_vmemmap(phys_addr_t base, phys_addr_t size);
> memblock does not care about vmemmap, please drop _vmemmap here and below as well.
>
>> void memblock_free_all(void);
>> void memblock_free(void *ptr, size_t size);
>> @@ -259,6 +264,11 @@ static inline bool memblock_is_nomap(struct memblock_region *m)
>> return m->flags & MEMBLOCK_NOMAP;
>> }
>>
>> +static inline bool memblock_is_noinit_vmemmap(struct memblock_region *m)
> memblock_is_reserved_noinit please.
>
>> +{
>> + return m->flags & MEMBLOCK_RSRV_NOINIT_VMEMMAP;
>> +}
>> +
>> 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 43cb4404d94c..a9782228c840 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -991,6 +991,23 @@ int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
>> return memblock_setclr_flag(&memblock.memory, base, size, 0, MEMBLOCK_NOMAP);
>> }
>>
>> +/**
>> + * memblock_reserved_mark_noinit_vmemmap - Mark a reserved memory region with flag
>> + * MEMBLOCK_RSRV_NOINIT_VMEMMAP.
> this should be about what marking RSRV_NOINIT does, not what flag it uses
>
>> + * @base: the base phys addr of the region
>> + * @size: the size of the region
>> + *
>> + * struct pages will not be initialized for reserved memory regions marked with
>> + * %MEMBLOCK_RSRV_NOINIT_VMEMMAP.
>> + *
>> + * Return: 0 on success, -errno on failure.
>> + */
>> +int __init_memblock memblock_reserved_mark_noinit_vmemmap(phys_addr_t base, phys_addr_t size)
>> +{
>> + return memblock_setclr_flag(&memblock.reserved, base, size, 1,
>> + MEMBLOCK_RSRV_NOINIT_VMEMMAP);
>> +}
>> +
>> static bool should_skip_region(struct memblock_type *type,
>> struct memblock_region *m,
>> int nid, int flags)
>> @@ -2107,13 +2124,18 @@ 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_VMEMMAP flag set
>> + */
>> for_each_reserved_mem_region(region) {
>> - nid = memblock_get_region_node(region);
>> - start = region->base;
>> - end = start + region->size;
>> + if (!memblock_is_noinit_vmemmap(region)) {
>> + nid = memblock_get_region_node(region);
>> + start = region->base;
>> + end = start + region->size;
>>
>> - reserve_bootmem_region(start, end, nid);
>> + reserve_bootmem_region(start, end, nid);
>> + }
>> }
>> }
>>
>> --
>> 2.25.1
>>
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