arm64/sparsemem: reduce SECTION_SIZE_BITS
Subsystems (2)
cover arm64/sparsemem: reduce SECTION_SIZE_BITS
This patch is the follow-up from the discussions in the thread [1]. Reducing the section size has the merit of reducing wastage of reserved memory for vmmemmap mappings for sections with large memory holes. Also with smaller section size gives more grunularity and agility for memory hot(un)plugging.
But there are also constraints in reducing SECTION_SIZE_BIT:
- Should accommodate highest order page for a given config
- Should not break PMD mapping in vmemmap for 4K pages
- Should not consume too many page->flags bits reducing space for other info
This patch uses the suggestions from Anshuman Khandual and David Hildenbrand in thread [1] to set the least possible section size to 128MB for 4K and 16K base page size configs for simplicity, and to 512MB for 64K base page size config.
[1] https://lore.kernel.org/lkml/[email protected]/T/#m8ee60ae69db5e9eb06ca7999c43828d49ccb9626
Sudarshan Rajagopalan (1):
arm64/sparsemem: reduce SECTION_SIZE_BITS
arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
Signature · 2 lines
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
PATCH 1/1 arm64/sparsemem: reduce SECTION_SIZE_BITS
memory_block_size_bytes() determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here being MIN_MEMORY_BLOCK_SIZE (1UL << SECTION_SIZE_BITS) for memory_block_size_bytes() on platforms like arm64 that does not override.
Current SECTION_SIZE_BITS is 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.
A section size bits selection must follow:
(MAX_ORDER - 1 + PAGE_SHIFT) <= SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDER is always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS = (CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT)
SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS = 29 (14 - 1 + 16) i.e 512MB for 64K pages with THP
But there are other problems in reducing SECTION_SIZE_BIT. Reducing it by too much would over populate /sys/devices/system/memory/ and also consume too many page->flags bits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping with CONFIG_ARM64_4K_PAGES.
Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
--- arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
arch/arm64/include/asm/sparsemem.h +21 -2
@@ -7,7 +7,26 @@#ifdef CONFIG_SPARSEMEM #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS -#define SECTION_SIZE_BITS 30 -#endif + +/* +* Section size must be at least 512MB for 64K base +* page size config. Otherwise it will be less than +* (MAX_ORDER - 1) and the build process will fail. +*/ +#ifdef CONFIG_ARM64_64K_PAGES +#define SECTION_SIZE_BITS 29 + +#else + +/* +* Section size must be at least 128MB for 4K base +* page size config. Otherwise PMD based huge page +* entries could not be created for vmemmap mappings. +* 16K follows 4K for simplicity. +*/ +#define SECTION_SIZE_BITS 27 +#endif /* CONFIG_ARM64_64K_PAGES */ + +#endif /* CONFIG_SPARSEMEM*/ #endif
Signature · 2 lines
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
Quoted 4 lines · Sudarshan Rajagopalan
But there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.
There is also the issue of requiring more space in the TLB cache with smaller page sizes. Or does ARM resolve these into smaller TLB entries anyways (going on my x86 kwon how here)? Anyways if there are only a few TLB entries then the effect could
be significant.
Will Deacon
maintainerQuoted 45 lines · Sudarshan Rajagopalan
memory_block_size_bytes()determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here beingMIN_MEMORY_BLOCK_SIZE(1UL <<SECTION_SIZE_BITS) formemory_block_size_bytes()on platforms like arm64 that does not override.Current
SECTION_SIZE_BITSis 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.A section size bits selection must follow:
(MAX_ORDER- 1 +PAGE_SHIFT) <=SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDERis always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS= (CONFIG_FORCE_MAX_ZONEORDER- 1 +PAGE_SHIFT)SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS= 29 (14 - 1 + 16) i.e 512MB for 64K pages with THPBut there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
Signed-off-by Sudarshan Rajagopalan <[email protected]>Suggested-by Anshuman Khandual <[email protected]>Suggested-by David Hildenbrand <[email protected]>Cc Catalin Marinas <[email protected]>Cc Will Deacon <[email protected]>Cc Anshuman Khandual <[email protected]>Cc David Hildenbrand <[email protected]>Cc Mike Rapoport <[email protected]>Cc Mark Rutland <[email protected]>Cc Logan Gunthorpe <[email protected]>Cc Andrew Morton <[email protected]>Cc Steven Price <[email protected]>Cc Suren Baghdasaryan <[email protected]>
Quoted 3 lines
--- arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
Anshuman -- are you happy with this now?
Will
Quoted 73 lines · Sudarshan Rajagopalan
memory_block_size_bytes()determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here beingMIN_MEMORY_BLOCK_SIZE(1UL <<SECTION_SIZE_BITS) formemory_block_size_bytes()on platforms like arm64 that does not override.Current
SECTION_SIZE_BITSis 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.A section size bits selection must follow:
(MAX_ORDER- 1 +PAGE_SHIFT) <=SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDERis always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS= (CONFIG_FORCE_MAX_ZONEORDER- 1 +PAGE_SHIFT)SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS= 29 (14 - 1 + 16) i.e 512MB for 64K pages with THPBut there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
Signed-off-by Sudarshan Rajagopalan <[email protected]>Suggested-by Anshuman Khandual <[email protected]>Suggested-by David Hildenbrand <[email protected]>Cc Catalin Marinas <[email protected]>Cc Will Deacon <[email protected]>Cc Anshuman Khandual <[email protected]>Cc David Hildenbrand <[email protected]>Cc Mike Rapoport <[email protected]>Cc Mark Rutland <[email protected]>Cc Logan Gunthorpe <[email protected]>Cc Andrew Morton <[email protected]>Cc Steven Price <[email protected]>Cc Suren Baghdasaryan <[email protected]>--- arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)arch/arm64/include/asm/sparsemem.h +13
-2@@ -7,7 +7,26 @@#ifdef CONFIG_SPARSEMEM #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS -#define SECTION_SIZE_BITS 30 -#endif + +/* +* Section size must be at least 512MB for 64K base +* page size config. Otherwise it will be less than +* (MAX_ORDER - 1) and the build process will fail. +*/ +#ifdef CONFIG_ARM64_64K_PAGES +#define SECTION_SIZE_BITS 29 + +#else + +/* +* Section size must be at least 128MB for 4K base
arch/arm64/include/asm/sparsemem.h line 32
Quoted 10 lines
arch/arm64/include/asm/sparsemem.h +8
-0+* page size config. Otherwise PMD based huge page +* entries could not be created for vmemmap mappings. +* 16K follows 4K for simplicity. +*/ +#define SECTION_SIZE_BITS 27 +#endif /* CONFIG_ARM64_64K_PAGES */ + +#endif /* CONFIG_SPARSEMEM*/ #endif
I'm happy to see this change.
Signature · 3 lines
Thanks, David / dhildenb
Quoted 32 lines · Sudarshan Rajagopalan
memory_block_size_bytes()determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here beingMIN_MEMORY_BLOCK_SIZE(1UL <<SECTION_SIZE_BITS) formemory_block_size_bytes()on platforms like arm64 that does not override.Current
SECTION_SIZE_BITSis 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.A section size bits selection must follow:
(MAX_ORDER- 1 +PAGE_SHIFT) <=SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDERis always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS= (CONFIG_FORCE_MAX_ZONEORDER- 1 +PAGE_SHIFT)SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS= 29 (14 - 1 + 16) i.e 512MB for 64K pages with THPBut there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
Quoted 13 lines
Signed-off-by Sudarshan Rajagopalan <[email protected]>Suggested-by Anshuman Khandual <[email protected]>Suggested-by David Hildenbrand <[email protected]>Cc Catalin Marinas <[email protected]>Cc Will Deacon <[email protected]>Cc Anshuman Khandual <[email protected]>Cc David Hildenbrand <[email protected]>Cc Mike Rapoport <[email protected]>Cc Mark Rutland <[email protected]>Cc Logan Gunthorpe <[email protected]>Cc Andrew Morton <[email protected]>Cc Steven Price <[email protected]>Cc Suren Baghdasaryan <[email protected]>
BTW, after reduction of the section size maybe arm64 should consider opting out of freeing unused memory map.
This will make David even more happy as this will allow dropping custom pfn_valid() ;-)
Quoted 41 lines
--- arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)arch/arm64/include/asm/sparsemem.h +21
-2@@ -7,7 +7,26 @@#ifdef CONFIG_SPARSEMEM #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS -#define SECTION_SIZE_BITS 30 -#endif + +/* +* Section size must be at least 512MB for 64K base +* page size config. Otherwise it will be less than +* (MAX_ORDER - 1) and the build process will fail. +*/ +#ifdef CONFIG_ARM64_64K_PAGES +#define SECTION_SIZE_BITS 29 + +#else + +/* +* Section size must be at least 128MB for 4K base +* page size config. Otherwise PMD based huge page +* entries could not be created for vmemmap mappings. +* 16K follows 4K for simplicity. +*/ +#define SECTION_SIZE_BITS 27 +#endif /* CONFIG_ARM64_64K_PAGES */ + +#endif /* CONFIG_SPARSEMEM*/ #endif Signature · 2 lines
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
Signature · 2 lines
Sincerely yours, Mike.
Quoted 32 lines · Sudarshan Rajagopalan
memory_block_size_bytes()determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here beingMIN_MEMORY_BLOCK_SIZE(1UL <<SECTION_SIZE_BITS) formemory_block_size_bytes()on platforms like arm64 that does not override.Current
SECTION_SIZE_BITSis 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.A section size bits selection must follow:
(MAX_ORDER- 1 +PAGE_SHIFT) <=SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDERis always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS= (CONFIG_FORCE_MAX_ZONEORDER- 1 +PAGE_SHIFT)SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS= 29 (14 - 1 + 16) i.e 512MB for 64K pages with THPBut there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
Quoted 13 lines
Signed-off-by Sudarshan Rajagopalan <[email protected]>Suggested-by Anshuman Khandual <[email protected]>Suggested-by David Hildenbrand <[email protected]>Cc Catalin Marinas <[email protected]>Cc Will Deacon <[email protected]>Cc Anshuman Khandual <[email protected]>Cc David Hildenbrand <[email protected]>Cc Mike Rapoport <[email protected]>Cc Mark Rutland <[email protected]>Cc Logan Gunthorpe <[email protected]>Cc Andrew Morton <[email protected]>Cc Steven Price <[email protected]>Cc Suren Baghdasaryan <[email protected]>
Catalin Marinas
maintainerQuoted 7 lines · Christoph Lameter
Quoted 4 lines · Sudarshan Rajagopalan
But there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.
Quoted 5 lines
There is also the issue of requiring more space in the TLB cache with smaller page sizes. Or does ARM resolve these into smaller TLB entries anyways (going on my x86 kwon how here)? Anyways if there are only a few TLB entries then the effect could
be significant.
There is indeed more TLB pressure with smaller page sizes but this patch doesn't change this.
Signature · 1 line
Catalin
Quoted 47 lines · Mike Rapoport
Quoted 32 lines · Sudarshan Rajagopalan
memory_block_size_bytes()determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here beingMIN_MEMORY_BLOCK_SIZE(1UL <<SECTION_SIZE_BITS) formemory_block_size_bytes()on platforms like arm64 that does not override.Current
SECTION_SIZE_BITSis 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.A section size bits selection must follow:
(MAX_ORDER- 1 +PAGE_SHIFT) <=SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDERis always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS= (CONFIG_FORCE_MAX_ZONEORDER- 1 +PAGE_SHIFT)SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS= 29 (14 - 1 + 16) i.e 512MB for 64K pages with THPBut there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
Quoted 13 lines
Signed-off-by Sudarshan Rajagopalan <[email protected]>Suggested-by Anshuman Khandual <[email protected]>Suggested-by David Hildenbrand <[email protected]>Cc Catalin Marinas <[email protected]>Cc Will Deacon <[email protected]>Cc Anshuman Khandual <[email protected]>Cc David Hildenbrand <[email protected]>Cc Mike Rapoport <[email protected]>Cc Mark Rutland <[email protected]>Cc Logan Gunthorpe <[email protected]>Cc Andrew Morton <[email protected]>Cc Steven Price <[email protected]>Cc Suren Baghdasaryan <[email protected]>
Quoted 7 lines
Acked-by Mike Rapoport <[email protected]>BTW, after reduction of the section size maybe arm64 should consider opting out of freeing unused memory map.
This will make David even more happy as this will allow dropping custom
pfn_valid();-)
Mike knows my wildest dreams ;)
Signature · 3 lines
Thanks, David / dhildenb
Quoted 8 lines · Sudarshan Rajagopalan
This patch is the follow-up from the discussions in the thread [1]. Reducing the section size has the merit of reducing wastage of reserved memory for vmmemmap mappings for sections with large memory holes. Also with smaller section size gives more grunularity and agility for memory hot(un)plugging.
But there are also constraints in reducing
SECTION_SIZE_BIT:[...]
Applied to arm64 (for-next/misc), thanks!
[1/1] arm64/sparsemem: reduce SECTION_SIZE_BITS
https://git.kernel.org/arm64/c/f0b13ee23241
Cheers,
Signature · 5 lines
Will https://fixes.arm64.dev https://next.arm64.dev https://will.arm64.dev
Anshuman Khandual
Reviewed-byQuoted 50 lines · Will Deacon
Quoted 45 lines · Sudarshan Rajagopalan
memory_block_size_bytes()determines the memory hotplug granularity i.e the amount of memory which can be hot added or hot removed from the kernel. The generic value here beingMIN_MEMORY_BLOCK_SIZE(1UL <<SECTION_SIZE_BITS) formemory_block_size_bytes()on platforms like arm64 that does not override.Current
SECTION_SIZE_BITSis 30 i.e 1GB which is large and a reduction here increases memory hotplug granularity, thus improving its agility. A reduced section size also reduces memory wastage in vmemmmap mapping for sections with large memory holes. So we try to set the least section size as possible.A section size bits selection must follow:
(MAX_ORDER- 1 +PAGE_SHIFT) <=SECTION_SIZE_BITS
CONFIG_FORCE_MAX_ZONEORDERis always defined on arm64 and so just following it would help achieve the smallest section size.
SECTION_SIZE_BITS= (CONFIG_FORCE_MAX_ZONEORDER- 1 +PAGE_SHIFT)SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
SECTION_SIZE_BITS= 29 (14 - 1 + 16) i.e 512MB for 64K pages with THPBut there are other problems in reducing
SECTION_SIZE_BIT. Reducing it by too much would over populate/sys/devices/system/memory/and also consume too manypage->flagsbits in the !vmemmap case. Also section size needs to be multiple of 128MB to have PMD based vmemmap mapping withCONFIG_ARM64_4K_PAGES.Given these constraints, lets just reduce the section size to 128MB for 4K and 16K base page size configs, and to 512MB for 64K base page size config.
Signed-off-by Sudarshan Rajagopalan <[email protected]>Suggested-by Anshuman Khandual <[email protected]>Suggested-by David Hildenbrand <[email protected]>Cc Catalin Marinas <[email protected]>Cc Will Deacon <[email protected]>Cc Anshuman Khandual <[email protected]>Cc David Hildenbrand <[email protected]>Cc Mike Rapoport <[email protected]>Cc Mark Rutland <[email protected]>Cc Logan Gunthorpe <[email protected]>Cc Andrew Morton <[email protected]>Cc Steven Price <[email protected]>Cc Suren Baghdasaryan <[email protected]>Quoted 3 lines
--- arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
Quoted 1 line
Anshuman -- are you happy with this now?
Yes.
A small nit. There are couple of extra lines in the patch which can be dropped, probably while merging.
Quoted 11 lines · Will Deacon
Quoted 8 lines · Sudarshan Rajagopalan
This patch is the follow-up from the discussions in the thread [1]. Reducing the section size has the merit of reducing wastage of reserved memory for vmmemmap mappings for sections with large memory holes. Also with smaller section size gives more grunularity and agility for memory hot(un)plugging.
But there are also constraints in reducing
SECTION_SIZE_BIT:[...]
Applied to arm64 (for-next/misc), thanks!
We have been using 128M for 4K pages for a while, using patch [1] without issues.
One thing that needs to be also modified is makedumpfile [2]- line 76, must update it SECTIONS_SIZE_BITS based on the PAGESIZE.
[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://sourceforge.net/p/makedumpfile/code/ci/master/tree/arch/arm64.c
Quoted 6 lines
[1/1] arm64/sparsemem: reduce
SECTION_SIZE_BITShttps://git.kernel.org/arm64/c/f0b13ee23241Cheers,