[PATCH v2 1/2] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[PATCH v2 1/2] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[Aneesh Kumar K.V]

commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound
devmaps") added support for using optimized vmmemap for devdax devices. But how
vmemmap mappings are created are architecture specific. For example, powerpc
with hash translation doesn't have vmemmap mappings in init_mm page table
instead they are bolted table entries in the hardware page table

vmemmap_populate_compound_pages() used by vmemmap optimization code is not aware
of these architecture-specific mapping. Hence allow architecture to opt for this
feature. I selected architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP
option as also supporting this feature.

This patch fixes the below crash on ppc64.

BUG: Unable to handle kernel data access on write at 0xc00c000100400038
Faulting instruction address: 0xc000000001269d90
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
Modules linked in:
CPU: 7 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc5-150500.34-default+ #2 5c90a668b6bbd142599890245c2fb5de19d7d28a
Hardware name: IBM,9009-42G POWER9 (raw) 0x4e0202 0xf000005 of:IBM,FW950.40 (VL950_099) hv:phyp pSeries
NIP:  c000000001269d90 LR: c0000000004c57d4 CTR: 0000000000000000
REGS: c000000003632c30 TRAP: 0300   Not tainted  (6.3.0-rc5-150500.34-default+)
MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 24842228  XER: 00000000
CFAR: c0000000004c57d0 DAR: c00c000100400038 DSISR: 42000000 IRQMASK: 0
....
NIP [c000000001269d90] __init_single_page.isra.74+0x14/0x4c
LR [c0000000004c57d4] __init_zone_device_page+0x44/0xd0
Call Trace:
[c000000003632ed0] [c000000003632f60] 0xc000000003632f60 (unreliable)
[c000000003632f10] [c0000000004c5ca0] memmap_init_zone_device+0x170/0x250
[c000000003632fe0] [c0000000005575f8] memremap_pages+0x2c8/0x7f0
[c0000000036330c0] [c000000000557b5c] devm_memremap_pages+0x3c/0xa0
[c000000003633100] [c000000000d458a8] dev_dax_probe+0x108/0x3e0
[c0000000036331a0] [c000000000d41430] dax_bus_probe+0xb0/0x140
[c0000000036331d0] [c000000000cef27c] really_probe+0x19c/0x520
[c000000003633260] [c000000000cef6b4] __driver_probe_device+0xb4/0x230
[c0000000036332e0] [c000000000cef888] driver_probe_device+0x58/0x120
[c000000003633320] [c000000000cefa6c] __device_attach_driver+0x11c/0x1e0
[c0000000036333a0] [c000000000cebc58] bus_for_each_drv+0xa8/0x130
[c000000003633400] [c000000000ceefcc] __device_attach+0x15c/0x250
[c0000000036334a0] [c000000000ced458] bus_probe_device+0x108/0x110
[c0000000036334f0] [c000000000ce92dc] device_add+0x7fc/0xa10
[c0000000036335b0] [c000000000d447c8] devm_create_dev_dax+0x1d8/0x530
[c000000003633640] [c000000000d46b60] __dax_pmem_probe+0x200/0x270
[c0000000036337b0] [c000000000d46bf0] dax_pmem_probe+0x20/0x70
[c0000000036337d0] [c000000000d2279c] nvdimm_bus_probe+0xac/0x2b0
[c000000003633860] [c000000000cef27c] really_probe+0x19c/0x520
[c0000000036338f0] [c000000000cef6b4] __driver_probe_device+0xb4/0x230
[c000000003633970] [c000000000cef888] driver_probe_device+0x58/0x120
[c0000000036339b0] [c000000000cefd08] __driver_attach+0x1d8/0x240
[c000000003633a30] [c000000000cebb04] bus_for_each_dev+0xb4/0x130
[c000000003633a90] [c000000000cee564] driver_attach+0x34/0x50
[c000000003633ab0] [c000000000ced878] bus_add_driver+0x218/0x300
[c000000003633b40] [c000000000cf1144] driver_register+0xa4/0x1b0
[c000000003633bb0] [c000000000d21a0c] __nd_driver_register+0x5c/0x100
[c000000003633c10] [c00000000206a2e8] dax_pmem_init+0x34/0x48
[c000000003633c30] [c0000000000132d0] do_one_initcall+0x60/0x320
[c000000003633d00] [c0000000020051b0] kernel_init_freeable+0x360/0x400
[c000000003633de0] [c000000000013764] kernel_init+0x34/0x1d0
[c000000003633e50] [c00000000000de14] ret_from_kernel_thread+0x5c/0x64

Fixes: 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound devmaps")
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Reported-by: Tarun Sahu <tsahu@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
changes from V1: 
* Only disable memory saving part of compound devmaps
* Update the correct Fixes: commit
* Add patch to drop HUGETLB specific kconfig

 include/linux/mm.h  | 16 ++++++++++++++++
 mm/page_alloc.c     |  9 ++++++---
 mm/sparse-vmemmap.c |  3 +--
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 716d30d93616..c47f2186d2c2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3442,6 +3442,22 @@ void vmemmap_populate_print_last(void);
 void vmemmap_free(unsigned long start, unsigned long end,
 		struct vmem_altmap *altmap);
 #endif
+
+#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMA
+static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
+					   struct dev_pagemap *pgmap)
+{
+	return is_power_of_2(sizeof(struct page)) &&
+		pgmap && (pgmap_vmemmap_nr(pgmap) > 1) && !altmap;
+}
+#else
+static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
+					   struct dev_pagemap *pgmap)
+{
+	return false;
+}
+#endif
+
 void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
 				  unsigned long nr_pages);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3bb3484563ed..292411d8816f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6844,10 +6844,13 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
  * of an altmap. See vmemmap_populate_compound_pages().
  */
 static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
+					      struct dev_pagemap *pgmap,
 					      unsigned long nr_pages)
 {
-	return is_power_of_2(sizeof(struct page)) &&
-		!altmap ? 2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
+	if (vmemmap_can_optimize(altmap, pgmap))
+		return 2 * (PAGE_SIZE / sizeof(struct page));
+	else
+		return nr_pages;
 }
 
 static void __ref memmap_init_compound(struct page *head,
@@ -6912,7 +6915,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 			continue;
 
 		memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
-				     compound_nr_pages(altmap, pfns_per_compound));
+				     compound_nr_pages(altmap, pgmap, pfns_per_compound));
 	}
 
 	pr_info("%s initialised %lu pages in %ums\n", __func__,
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index c5398a5960d0..10d73a0dfcec 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -458,8 +458,7 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
 		return NULL;
 
-	if (is_power_of_2(sizeof(struct page)) &&
-	    pgmap && pgmap_vmemmap_nr(pgmap) > 1 && !altmap)
+	if (vmemmap_can_optimize(altmap, pgmap))
 		r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap);
 	else
 		r = vmemmap_populate(start, end, nid, altmap);
-- 
2.39.2

[PATCH v2 2/2] m/hugetlb: Rename ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

[Aneesh Kumar K.V]

Now we use ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP config option
to indicate devdax and hugetlb vmemmap optimization support. Hence
rename that to a generic ARCH_WANT_OPTIMIZE_VMEMMAP

Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 arch/arm64/Kconfig     | 2 +-
 arch/loongarch/Kconfig | 2 +-
 arch/s390/Kconfig      | 2 +-
 arch/x86/Kconfig       | 2 +-
 fs/Kconfig             | 9 +--------
 include/linux/mm.h     | 2 +-
 mm/Kconfig             | 6 ++++++
 7 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 27b2592698b0..77d9713dcd9c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -100,9 +100,9 @@ config ARM64
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
-	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_NO_INSTR
+	select ARCH_WANT_OPTIMIZE_VMEMMAP
 	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARM_AMBA
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 9cc8b84f7eb0..9cb00f962de1 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -53,9 +53,9 @@ config LOONGARCH
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
-	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_NO_INSTR
+	select ARCH_WANT_OPTIMIZE_VMEMMAP
 	select BUILDTIME_TABLE_SORT
 	select COMMON_CLK
 	select CPU_PM
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 933771b0b07a..df2cd510480a 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -126,7 +126,7 @@ config S390
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANT_DEFAULT_BPF_JIT
 	select ARCH_WANT_IPC_PARSE_VERSION
-	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+	select ARCH_WANT_OPTIMIZE_VMEMMAP
 	select BUILDTIME_TABLE_SORT
 	select CLONE_BACKWARDS2
 	select DMA_OPS if PCI
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a825bf031f49..5269131cc248 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -125,8 +125,8 @@ config X86
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANT_GENERAL_HUGETLB
 	select ARCH_WANT_HUGE_PMD_SHARE
-	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP	if X86_64
 	select ARCH_WANT_LD_ORPHAN_WARN
+	select ARCH_WANT_OPTIMIZE_VMEMMAP	if X86_64
 	select ARCH_WANTS_THP_SWAP		if X86_64
 	select ARCH_HAS_PARANOID_L1D_FLUSH
 	select BUILDTIME_TABLE_SORT
diff --git a/fs/Kconfig b/fs/Kconfig
index e99830c65033..cc07a0cd3172 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -250,16 +250,9 @@ config HUGETLBFS
 config HUGETLB_PAGE
 	def_bool HUGETLBFS
 
-#
-# Select this config option from the architecture Kconfig, if it is preferred
-# to enable the feature of HugeTLB Vmemmap Optimization (HVO).
-#
-config ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-	bool
-
 config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	def_bool HUGETLB_PAGE
-	depends on ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+	depends on ARCH_WANT_OPTIMIZE_VMEMMAP
 	depends on SPARSEMEM_VMEMMAP
 
 config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c47f2186d2c2..fb71e21df23d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3443,7 +3443,7 @@ void vmemmap_free(unsigned long start, unsigned long end,
 		struct vmem_altmap *altmap);
 #endif
 
-#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMA
+#ifdef CONFIG_ARCH_WANT_OPTIMIZE_VMEMMAP
 static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
 					   struct dev_pagemap *pgmap)
 {
diff --git a/mm/Kconfig b/mm/Kconfig
index ff7b209dec05..492919cf62a4 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -460,6 +460,12 @@ config SPARSEMEM_VMEMMAP
 	  SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
 	  pfn_to_page and page_to_pfn operations.  This is the most
 	  efficient option when sufficient kernel resources are available.
+#
+# Select this config option from the architecture Kconfig, if it is preferred
+# to enable the feature of HugeTLB/dev_dax vmemmap optimization.
+#
+config ARCH_WANT_OPTIMIZE_VMEMMAP
+	bool
 
 config HAVE_MEMBLOCK_PHYS_MAP
 	bool
-- 
2.39.2

Re: [PATCH v2 1/2] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[Joao Martins]

On 11/04/2023 15:18, Aneesh Kumar K.V wrote:
> commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound
> devmaps") added support for using optimized vmmemap for devdax devices. But how
> vmemmap mappings are created are architecture specific. For example, powerpc
> with hash translation doesn't have vmemmap mappings in init_mm page table
> instead they are bolted table entries in the hardware page table
> 
> vmemmap_populate_compound_pages() used by vmemmap optimization code is not aware
> of these architecture-specific mapping. Hence allow architecture to opt for this
> feature. I selected architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> option as also supporting this feature.
> 
Perhaps rephrase last sentence to be in imperative form e.g.:

Architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP option are selected when
supporting this feature.

> This patch fixes the below crash on ppc64.
> 
Avoid the 'This patch' per submission guidelines e.g.

'On ppc64 (pmem) where this isn't supported, it fixes below crash:'

> BUG: Unable to handle kernel data access on write at 0xc00c000100400038
> Faulting instruction address: 0xc000000001269d90
> Oops: Kernel access of bad area, sig: 11 [#1]
> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> Modules linked in:
> CPU: 7 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc5-150500.34-default+ #2 5c90a668b6bbd142599890245c2fb5de19d7d28a
> Hardware name: IBM,9009-42G POWER9 (raw) 0x4e0202 0xf000005 of:IBM,FW950.40 (VL950_099) hv:phyp pSeries
> NIP:  c000000001269d90 LR: c0000000004c57d4 CTR: 0000000000000000
> REGS: c000000003632c30 TRAP: 0300   Not tainted  (6.3.0-rc5-150500.34-default+)
> MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 24842228  XER: 00000000
> CFAR: c0000000004c57d0 DAR: c00c000100400038 DSISR: 42000000 IRQMASK: 0
> ....
> NIP [c000000001269d90] __init_single_page.isra.74+0x14/0x4c
> LR [c0000000004c57d4] __init_zone_device_page+0x44/0xd0
> Call Trace:
> [c000000003632ed0] [c000000003632f60] 0xc000000003632f60 (unreliable)
> [c000000003632f10] [c0000000004c5ca0] memmap_init_zone_device+0x170/0x250
> [c000000003632fe0] [c0000000005575f8] memremap_pages+0x2c8/0x7f0
> [c0000000036330c0] [c000000000557b5c] devm_memremap_pages+0x3c/0xa0
> [c000000003633100] [c000000000d458a8] dev_dax_probe+0x108/0x3e0
> [c0000000036331a0] [c000000000d41430] dax_bus_probe+0xb0/0x140
> [c0000000036331d0] [c000000000cef27c] really_probe+0x19c/0x520
> [c000000003633260] [c000000000cef6b4] __driver_probe_device+0xb4/0x230
> [c0000000036332e0] [c000000000cef888] driver_probe_device+0x58/0x120
> [c000000003633320] [c000000000cefa6c] __device_attach_driver+0x11c/0x1e0
> [c0000000036333a0] [c000000000cebc58] bus_for_each_drv+0xa8/0x130
> [c000000003633400] [c000000000ceefcc] __device_attach+0x15c/0x250
> [c0000000036334a0] [c000000000ced458] bus_probe_device+0x108/0x110
> [c0000000036334f0] [c000000000ce92dc] device_add+0x7fc/0xa10
> [c0000000036335b0] [c000000000d447c8] devm_create_dev_dax+0x1d8/0x530
> [c000000003633640] [c000000000d46b60] __dax_pmem_probe+0x200/0x270
> [c0000000036337b0] [c000000000d46bf0] dax_pmem_probe+0x20/0x70
> [c0000000036337d0] [c000000000d2279c] nvdimm_bus_probe+0xac/0x2b0
> [c000000003633860] [c000000000cef27c] really_probe+0x19c/0x520
> [c0000000036338f0] [c000000000cef6b4] __driver_probe_device+0xb4/0x230
> [c000000003633970] [c000000000cef888] driver_probe_device+0x58/0x120
> [c0000000036339b0] [c000000000cefd08] __driver_attach+0x1d8/0x240
> [c000000003633a30] [c000000000cebb04] bus_for_each_dev+0xb4/0x130
> [c000000003633a90] [c000000000cee564] driver_attach+0x34/0x50
> [c000000003633ab0] [c000000000ced878] bus_add_driver+0x218/0x300
> [c000000003633b40] [c000000000cf1144] driver_register+0xa4/0x1b0
> [c000000003633bb0] [c000000000d21a0c] __nd_driver_register+0x5c/0x100
> [c000000003633c10] [c00000000206a2e8] dax_pmem_init+0x34/0x48
> [c000000003633c30] [c0000000000132d0] do_one_initcall+0x60/0x320
> [c000000003633d00] [c0000000020051b0] kernel_init_freeable+0x360/0x400
> [c000000003633de0] [c000000000013764] kernel_init+0x34/0x1d0
> [c000000003633e50] [c00000000000de14] ret_from_kernel_thread+0x5c/0x64
> 
> Fixes: 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound devmaps")
> Cc: Joao Martins <joao.m.martins@oracle.com>
> Cc: Muchun Song <songmuchun@bytedance.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Reported-by: Tarun Sahu <tsahu@linux.ibm.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
> changes from V1: 
> * Only disable memory saving part of compound devmaps
> * Update the correct Fixes: commit
> * Add patch to drop HUGETLB specific kconfig
> 
>  include/linux/mm.h  | 16 ++++++++++++++++
>  mm/page_alloc.c     |  9 ++++++---
>  mm/sparse-vmemmap.c |  3 +--
>  3 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 716d30d93616..c47f2186d2c2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3442,6 +3442,22 @@ void vmemmap_populate_print_last(void);
>  void vmemmap_free(unsigned long start, unsigned long end,
>  		struct vmem_altmap *altmap);
>  #endif
> +
> +#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMA

You are missing a 'P'

> +static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
> +					   struct dev_pagemap *pgmap)
> +{
> +	return is_power_of_2(sizeof(struct page)) &&
> +		pgmap && (pgmap_vmemmap_nr(pgmap) > 1) && !altmap;
> +}
> +#else
> +static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
> +					   struct dev_pagemap *pgmap)
> +{
> +	return false;
> +}
> +#endif
> +
>  void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
>  				  unsigned long nr_pages);
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3bb3484563ed..292411d8816f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6844,10 +6844,13 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
>   * of an altmap. See vmemmap_populate_compound_pages().
>   */
>  static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
> +					      struct dev_pagemap *pgmap,
>  					      unsigned long nr_pages)
>  {
> -	return is_power_of_2(sizeof(struct page)) &&
> -		!altmap ? 2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
> +	if (vmemmap_can_optimize(altmap, pgmap))
> +		return 2 * (PAGE_SIZE / sizeof(struct page));
> +	else
> +		return nr_pages;
>  }
>  

Keep the ternary operator as already is the case for compound_nr_pages to avoid
doing too much in one patch:

	return vmemmap_can_optimize(altmap, pgmap) ?
		2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;

Or you really want to remove the ternary operator perhaps take the unnecessary
else and make the long line be less indented:

	if (!vmemmap_can_optimize(altmap, pgmap))
		return nr_pages;

	return  2 * (PAGE_SIZE / sizeof(struct page));

I don't think the latter is a significant improvement over the ternary one. But
I guess that's a matter of preferred style.

>  static void __ref memmap_init_compound(struct page *head,
> @@ -6912,7 +6915,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
>  			continue;
>  
>  		memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
> -				     compound_nr_pages(altmap, pfns_per_compound));
> +				     compound_nr_pages(altmap, pgmap, pfns_per_compound));
>  	}
>  
>  	pr_info("%s initialised %lu pages in %ums\n", __func__,
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index c5398a5960d0..10d73a0dfcec 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -458,8 +458,7 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
>  		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
>  		return NULL;
>  
> -	if (is_power_of_2(sizeof(struct page)) &&
> -	    pgmap && pgmap_vmemmap_nr(pgmap) > 1 && !altmap)
> +	if (vmemmap_can_optimize(altmap, pgmap))
>  		r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap);
>  	else
>  		r = vmemmap_populate(start, end, nid, altmap);

Re: [PATCH v2 1/2] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[Aneesh Kumar K.V]

Joao Martins <joao.m.martins@oracle.com> writes:

> On 11/04/2023 15:18, Aneesh Kumar K.V wrote:
>> commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound
>> devmaps") added support for using optimized vmmemap for devdax devices. But how
>> vmemmap mappings are created are architecture specific. For example, powerpc
>> with hash translation doesn't have vmemmap mappings in init_mm page table
>> instead they are bolted table entries in the hardware page table
>> 
>> vmemmap_populate_compound_pages() used by vmemmap optimization code is not aware
>> of these architecture-specific mapping. Hence allow architecture to opt for this
>> feature. I selected architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>> option as also supporting this feature.
>> 
> Perhaps rephrase last sentence to be in imperative form e.g.:
>
> Architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP option are selected when
> supporting this feature.
>
>> This patch fixes the below crash on ppc64.
>> 
> Avoid the 'This patch' per submission guidelines e.g.
>
> 'On ppc64 (pmem) where this isn't supported, it fixes below crash:'

ok will update in the next version.

>
>> BUG: Unable to handle kernel data access on write at 0xc00c000100400038
>> Faulting instruction address: 0xc000000001269d90
>> Oops: Kernel access of bad area, sig: 11 [#1]
>> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
>> Modules linked in:
> 

...

>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 716d30d93616..c47f2186d2c2 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3442,6 +3442,22 @@ void vmemmap_populate_print_last(void);
>>  void vmemmap_free(unsigned long start, unsigned long end,
>>  		struct vmem_altmap *altmap);
>>  #endif
>> +
>> +#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMA
>
> You are missing a 'P'

I noticed that after sending v2 and sent v2-updated with that change. 

>
>> +static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
>> +					   struct dev_pagemap *pgmap)
>> +{
>> +	return is_power_of_2(sizeof(struct page)) &&
>> +		pgmap && (pgmap_vmemmap_nr(pgmap) > 1) && !altmap;
>> +}
>> +#else
>> +static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
>> +					   struct dev_pagemap *pgmap)
>> +{
>> +	return false;
>> +}
>> +#endif
>> +
>>  void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
>>  				  unsigned long nr_pages);
>>  
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 3bb3484563ed..292411d8816f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6844,10 +6844,13 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
>>   * of an altmap. See vmemmap_populate_compound_pages().
>>   */
>>  static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
>> +					      struct dev_pagemap *pgmap,
>>  					      unsigned long nr_pages)
>>  {
>> -	return is_power_of_2(sizeof(struct page)) &&
>> -		!altmap ? 2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
>> +	if (vmemmap_can_optimize(altmap, pgmap))
>> +		return 2 * (PAGE_SIZE / sizeof(struct page));
>> +	else
>> +		return nr_pages;
>>  }
>>  
>
> Keep the ternary operator as already is the case for compound_nr_pages to avoid
> doing too much in one patch:
>
> 	return vmemmap_can_optimize(altmap, pgmap) ?
> 		2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
>
> Or you really want to remove the ternary operator perhaps take the unnecessary
> else and make the long line be less indented:
>
> 	if (!vmemmap_can_optimize(altmap, pgmap))
> 		return nr_pages;
>
> 	return  2 * (PAGE_SIZE / sizeof(struct page));
>
> I don't think the latter is a significant improvement over the ternary one. But
> I guess that's a matter of preferred style.

How about

static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
					      struct dev_pagemap *pgmap)
{

	if (!vmemmap_can_optimize(altmap, pgmap))
		return pgmap_vmemmap_nr(pgmap);

	return 2 * (PAGE_SIZE / sizeof(struct page));
}



>
>>  static void __ref memmap_init_compound(struct page *head,
>> @@ -6912,7 +6915,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
>>  			continue;
>>  
>>  		memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
>> -				     compound_nr_pages(altmap, pfns_per_compound));
>> +				     compound_nr_pages(altmap, pgmap, pfns_per_compound));
>>  	}
>>  
>>  	pr_info("%s initialised %lu pages in %ums\n", __func__,
>> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
>> index c5398a5960d0..10d73a0dfcec 100644
>> --- a/mm/sparse-vmemmap.c
>> +++ b/mm/sparse-vmemmap.c
>> @@ -458,8 +458,7 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
>>  		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
>>  		return NULL;
>>  
>> -	if (is_power_of_2(sizeof(struct page)) &&
>> -	    pgmap && pgmap_vmemmap_nr(pgmap) > 1 && !altmap)
>> +	if (vmemmap_can_optimize(altmap, pgmap))
>>  		r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap);
>>  	else
>>  		r = vmemmap_populate(start, end, nid, altmap);

-aneesh

Re: [PATCH v2 1/2] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[Joao Martins]

On 11/04/2023 16:20, Aneesh Kumar K.V wrote:
> Joao Martins <joao.m.martins@oracle.com> writes:
>> On 11/04/2023 15:18, Aneesh Kumar K.V wrote:
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 3bb3484563ed..292411d8816f 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -6844,10 +6844,13 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
>>>   * of an altmap. See vmemmap_populate_compound_pages().
>>>   */
>>>  static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
>>> +					      struct dev_pagemap *pgmap,
>>>  					      unsigned long nr_pages)
>>>  {
>>> -	return is_power_of_2(sizeof(struct page)) &&
>>> -		!altmap ? 2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
>>> +	if (vmemmap_can_optimize(altmap, pgmap))
>>> +		return 2 * (PAGE_SIZE / sizeof(struct page));
>>> +	else
>>> +		return nr_pages;
>>>  }
>>>  
>>
>> Keep the ternary operator as already is the case for compound_nr_pages to avoid
>> doing too much in one patch:
>>
>> 	return vmemmap_can_optimize(altmap, pgmap) ?
>> 		2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
>>
>> Or you really want to remove the ternary operator perhaps take the unnecessary
>> else and make the long line be less indented:
>>
>> 	if (!vmemmap_can_optimize(altmap, pgmap))
>> 		return nr_pages;
>>
>> 	return  2 * (PAGE_SIZE / sizeof(struct page));
>>
>> I don't think the latter is a significant improvement over the ternary one. But
>> I guess that's a matter of preferred style.
> 
> How about
> 
> static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
> 					      struct dev_pagemap *pgmap)
> {
> 
> 	if (!vmemmap_can_optimize(altmap, pgmap))
> 		return pgmap_vmemmap_nr(pgmap);
> 
> 	return 2 * (PAGE_SIZE / sizeof(struct page));
> }
> 

I am a bit more fond of the ternary option. But this snip above is fine as well,
including with the s/nr_pages/pgmap_vmemmap_nr(pgmap)/ change you added.

Re: [PATCH v2 2/2] m/hugetlb: Rename ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

[Joao Martins]

[subject line should be mm/hugetlb as opposed to m/hugetlb]

On 11/04/2023 15:18, Aneesh Kumar K.V wrote:
> Now we use ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP config option
> to indicate devdax and hugetlb vmemmap optimization support. Hence
> rename that to a generic ARCH_WANT_OPTIMIZE_VMEMMAP
> 
> Cc: Joao Martins <joao.m.martins@oracle.com>
> Cc: Muchun Song <songmuchun@bytedance.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

+Mike from hugetlb

> ---
>  arch/arm64/Kconfig     | 2 +-
>  arch/loongarch/Kconfig | 2 +-
>  arch/s390/Kconfig      | 2 +-
>  arch/x86/Kconfig       | 2 +-
>  fs/Kconfig             | 9 +--------
>  include/linux/mm.h     | 2 +-
>  mm/Kconfig             | 6 ++++++
>  7 files changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 27b2592698b0..77d9713dcd9c 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -100,9 +100,9 @@ config ARM64
>  	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>  	select ARCH_WANT_FRAME_POINTERS
>  	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>  	select ARCH_WANT_LD_ORPHAN_WARN
>  	select ARCH_WANTS_NO_INSTR
> +	select ARCH_WANT_OPTIMIZE_VMEMMAP

Why don't you just change the line you just deleted?

>  	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>  	select ARM_AMBA
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 9cc8b84f7eb0..9cb00f962de1 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -53,9 +53,9 @@ config LOONGARCH
>  	select ARCH_USE_QUEUED_RWLOCKS
>  	select ARCH_USE_QUEUED_SPINLOCKS
>  	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>  	select ARCH_WANT_LD_ORPHAN_WARN
>  	select ARCH_WANTS_NO_INSTR
> +	select ARCH_WANT_OPTIMIZE_VMEMMAP

Same comment here

>  	select BUILDTIME_TABLE_SORT
>  	select COMMON_CLK
>  	select CPU_PM
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 933771b0b07a..df2cd510480a 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -126,7 +126,7 @@ config S390
>  	select ARCH_WANTS_NO_INSTR
>  	select ARCH_WANT_DEFAULT_BPF_JIT
>  	select ARCH_WANT_IPC_PARSE_VERSION
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> +	select ARCH_WANT_OPTIMIZE_VMEMMAP
>  	select BUILDTIME_TABLE_SORT
>  	select CLONE_BACKWARDS2
>  	select DMA_OPS if PCI

This one is good

> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index a825bf031f49..5269131cc248 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -125,8 +125,8 @@ config X86
>  	select ARCH_WANTS_NO_INSTR
>  	select ARCH_WANT_GENERAL_HUGETLB
>  	select ARCH_WANT_HUGE_PMD_SHARE
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP	if X86_64
>  	select ARCH_WANT_LD_ORPHAN_WARN
> +	select ARCH_WANT_OPTIMIZE_VMEMMAP	if X86_64
>  	select ARCH_WANTS_THP_SWAP		if X86_64
>  	select ARCH_HAS_PARANOID_L1D_FLUSH
>  	select BUILDTIME_TABLE_SORT

Same comment here

> diff --git a/fs/Kconfig b/fs/Kconfig
> index e99830c65033..cc07a0cd3172 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -250,16 +250,9 @@ config HUGETLBFS
>  config HUGETLB_PAGE
>  	def_bool HUGETLBFS
>  
> -#
> -# Select this config option from the architecture Kconfig, if it is preferred
> -# to enable the feature of HugeTLB Vmemmap Optimization (HVO).
> -#
> -config ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> -	bool
> -
>  config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>  	def_bool HUGETLB_PAGE
> -	depends on ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> +	depends on ARCH_WANT_OPTIMIZE_VMEMMAP
>  	depends on SPARSEMEM_VMEMMAP
>  
>  config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c47f2186d2c2..fb71e21df23d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3443,7 +3443,7 @@ void vmemmap_free(unsigned long start, unsigned long end,
>  		struct vmem_altmap *altmap);
>  #endif
>  
> -#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMA
> +#ifdef CONFIG_ARCH_WANT_OPTIMIZE_VMEMMAP
>  static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
>  					   struct dev_pagemap *pgmap)
>  {
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ff7b209dec05..492919cf62a4 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -460,6 +460,12 @@ config SPARSEMEM_VMEMMAP
>  	  SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
>  	  pfn_to_page and page_to_pfn operations.  This is the most
>  	  efficient option when sufficient kernel resources are available.
> +#
> +# Select this config option from the architecture Kconfig, if it is preferred
> +# to enable the feature of HugeTLB/dev_dax vmemmap optimization.
> +#
> +config ARCH_WANT_OPTIMIZE_VMEMMAP
> +	bool
>  
>  config HAVE_MEMBLOCK_PHYS_MAP
>  	bool

Re: [PATCH v2 2/2] m/hugetlb: Rename ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

[Aneesh Kumar K V]

On 4/11/23 9:22 PM, Joao Martins wrote:
> [subject line should be mm/hugetlb as opposed to m/hugetlb]
> 
> On 11/04/2023 15:18, Aneesh Kumar K.V wrote:
>> Now we use ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP config option
>> to indicate devdax and hugetlb vmemmap optimization support. Hence
>> rename that to a generic ARCH_WANT_OPTIMIZE_VMEMMAP
>>
>> Cc: Joao Martins <joao.m.martins@oracle.com>
>> Cc: Muchun Song <songmuchun@bytedance.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> 
> +Mike from hugetlb
> 
>> ---
>>  arch/arm64/Kconfig     | 2 +-
>>  arch/loongarch/Kconfig | 2 +-
>>  arch/s390/Kconfig      | 2 +-
>>  arch/x86/Kconfig       | 2 +-
>>  fs/Kconfig             | 9 +--------
>>  include/linux/mm.h     | 2 +-
>>  mm/Kconfig             | 6 ++++++
>>  7 files changed, 12 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 27b2592698b0..77d9713dcd9c 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -100,9 +100,9 @@ config ARM64
>>  	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>>  	select ARCH_WANT_FRAME_POINTERS
>>  	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
>> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>>  	select ARCH_WANT_LD_ORPHAN_WARN
>>  	select ARCH_WANTS_NO_INSTR
>> +	select ARCH_WANT_OPTIMIZE_VMEMMAP
> 
> Why don't you just change the line you just deleted?
> 

Those config select statements are sorted? 

-aneesh

Re: [PATCH v2 2/2] m/hugetlb: Rename ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

[Joao Martins]

On 11/04/2023 17:14, Aneesh Kumar K V wrote:
> On 4/11/23 9:22 PM, Joao Martins wrote:
>> [subject line should be mm/hugetlb as opposed to m/hugetlb]
>>
>> On 11/04/2023 15:18, Aneesh Kumar K.V wrote:
>>> Now we use ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP config option
>>> to indicate devdax and hugetlb vmemmap optimization support. Hence
>>> rename that to a generic ARCH_WANT_OPTIMIZE_VMEMMAP
>>>
>>> Cc: Joao Martins <joao.m.martins@oracle.com>
>>> Cc: Muchun Song <songmuchun@bytedance.com>
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>
>> +Mike from hugetlb
>>
>>> ---
>>>  arch/arm64/Kconfig     | 2 +-
>>>  arch/loongarch/Kconfig | 2 +-
>>>  arch/s390/Kconfig      | 2 +-
>>>  arch/x86/Kconfig       | 2 +-
>>>  fs/Kconfig             | 9 +--------
>>>  include/linux/mm.h     | 2 +-
>>>  mm/Kconfig             | 6 ++++++
>>>  7 files changed, 12 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index 27b2592698b0..77d9713dcd9c 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -100,9 +100,9 @@ config ARM64
>>>  	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>>>  	select ARCH_WANT_FRAME_POINTERS
>>>  	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
>>> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>>>  	select ARCH_WANT_LD_ORPHAN_WARN
>>>  	select ARCH_WANTS_NO_INSTR
>>> +	select ARCH_WANT_OPTIMIZE_VMEMMAP
>>
>> Why don't you just change the line you just deleted?
>>
> 
> Those config select statements are sorted? 

/me facepalm

Totally missed that.

Re: [External] [PATCH v2 2/2] m/hugetlb: Rename ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

[Muchun Song]

On Tue, Apr 11, 2023 at 10:18 PM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> Now we use ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP config option
> to indicate devdax and hugetlb vmemmap optimization support. Hence
> rename that to a generic ARCH_WANT_OPTIMIZE_VMEMMAP
>
> Cc: Joao Martins <joao.m.martins@oracle.com>
> Cc: Muchun Song <songmuchun@bytedance.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

I suggest rewording the prefix of subject to "mm/hugetlb_vmemmap:".
Renaming LGTM.

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.