[PATCH v3 0/3] mm, smaps: MMUPageSize for device-dax

[PATCH v3 0/3] mm, smaps: MMUPageSize for device-dax

[Dan Williams]

Changes since v2:
* Split the fix of the definition vma_mmu_pagesize() on powerpc to its
  own patch.

[1]: https://lists.01.org/pipermail/linux-nvdimm/2018-February/014101.html

---

Andrew,

Similar to commit 31383c6865a5 "mm, hugetlbfs: introduce ->split() to
vm_operations_struct" here is another occasion where we want
special-case hugetlbfs/hstate enabling to also apply to device-dax.

This begs the question what other hstate conversions we might do beyond
->split() and ->pagesize(), but this appears to be the last of the
usages of hstate_vma() in generic/non-hugetlbfs specific code paths.

---

Dan Williams (3):
      mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()
      mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct
      device-dax: implement ->pagesize() for smaps to report MMUPageSize


 arch/powerpc/include/asm/hugetlb.h |    6 ------
 arch/powerpc/mm/hugetlbpage.c      |    5 +----
 drivers/dax/device.c               |   10 ++++++++++
 include/linux/mm.h                 |    1 +
 mm/hugetlb.c                       |   27 ++++++++++++++-------------
 5 files changed, 26 insertions(+), 23 deletions(-)
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[PATCH v3 0/3] mm, smaps: MMUPageSize for device-dax

[Dan Williams]

Changes since v2:
* Split the fix of the definition vma_mmu_pagesize() on powerpc to its
  own patch.

[1]: https://lists.01.org/pipermail/linux-nvdimm/2018-February/014101.html

---

Andrew,

Similar to commit 31383c6865a5 "mm, hugetlbfs: introduce ->split() to
vm_operations_struct" here is another occasion where we want
special-case hugetlbfs/hstate enabling to also apply to device-dax.

This begs the question what other hstate conversions we might do beyond
->split() and ->pagesize(), but this appears to be the last of the
usages of hstate_vma() in generic/non-hugetlbfs specific code paths.

---

Dan Williams (3):
      mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()
      mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct
      device-dax: implement ->pagesize() for smaps to report MMUPageSize


 arch/powerpc/include/asm/hugetlb.h |    6 ------
 arch/powerpc/mm/hugetlbpage.c      |    5 +----
 drivers/dax/device.c               |   10 ++++++++++
 include/linux/mm.h                 |    1 +
 mm/hugetlb.c                       |   27 ++++++++++++++-------------
 5 files changed, 26 insertions(+), 23 deletions(-)

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[PATCH v3 1/3] mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()

[Dan Williams]

The current powerpc definition of vma_mmu_pagesize() open codes looking
up the page size via hstate. It is identical to the generic
vma_kernel_pagesize() implementation.

Now, vma_kernel_pagesize() is growing support for determining the
page size of Device-DAX vmas in addition to the existing Hugetlbfs page
size determination.

Ideally, if the powerpc vma_mmu_pagesize() used vma_kernel_pagesize() it
would automatically benefit from any new vma-type support that is added
to vma_kernel_pagesize(). However, the powerpc vma_mmu_pagesize() is
prevented from calling vma_kernel_pagesize() due to a circular header
dependency that requires vma_mmu_pagesize() to be defined before
including <linux/hugetlb.h>.

Break this circular dependency by defining the default
vma_mmu_pagesize() as a __weak symbol to be overridden by the powerpc
version.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/powerpc/include/asm/hugetlb.h |    6 ------
 arch/powerpc/mm/hugetlbpage.c      |    5 +----
 mm/hugetlb.c                       |    8 +++-----
 3 files changed, 4 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
index 1a4847f67ea8..6f6751d3eba9 100644
--- a/arch/powerpc/include/asm/hugetlb.h
+++ b/arch/powerpc/include/asm/hugetlb.h
@@ -118,12 +118,6 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb, unsigned long addr,
 			    unsigned long ceiling);
 
 /*
- * The version of vma_mmu_pagesize() in arch/powerpc/mm/hugetlbpage.c needs
- * to override the version in mm/hugetlb.c
- */
-#define vma_mmu_pagesize vma_mmu_pagesize
-
-/*
  * If the arch doesn't supply something else, assume that hugepage
  * size aligned regions are ok without further preparation.
  */
diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 876da2bc1796..3a08d211d2ee 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -568,10 +568,7 @@ unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 	if (!radix_enabled())
 		return 1UL << mmu_psize_to_shift(psize);
 #endif
-	if (!is_vm_hugetlb_page(vma))
-		return PAGE_SIZE;
-
-	return huge_page_size(hstate_vma(vma));
+	return vma_kernel_pagesize(vma);
 }
 
 static inline bool is_power_of_4(unsigned long x)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7c204e3d132b..f9c4ea42b04a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -650,15 +650,13 @@ EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 /*
  * Return the page size being used by the MMU to back a VMA. In the majority
  * of cases, the page size used by the kernel matches the MMU size. On
- * architectures where it differs, an architecture-specific version of this
- * function is required.
+ * architectures where it differs, an architecture-specific 'strong'
+ * version of this symbol is required.
  */
-#ifndef vma_mmu_pagesize
-unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
+__weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 {
 	return vma_kernel_pagesize(vma);
 }
-#endif
 
 /*
  * Flags for MAP_PRIVATE reservations.  These are stored in the bottom

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[PATCH v3 1/3] mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()

[Dan Williams]

The current powerpc definition of vma_mmu_pagesize() open codes looking
up the page size via hstate. It is identical to the generic
vma_kernel_pagesize() implementation.

Now, vma_kernel_pagesize() is growing support for determining the
page size of Device-DAX vmas in addition to the existing Hugetlbfs page
size determination.

Ideally, if the powerpc vma_mmu_pagesize() used vma_kernel_pagesize() it
would automatically benefit from any new vma-type support that is added
to vma_kernel_pagesize(). However, the powerpc vma_mmu_pagesize() is
prevented from calling vma_kernel_pagesize() due to a circular header
dependency that requires vma_mmu_pagesize() to be defined before
including <linux/hugetlb.h>.

Break this circular dependency by defining the default
vma_mmu_pagesize() as a __weak symbol to be overridden by the powerpc
version.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/powerpc/include/asm/hugetlb.h |    6 ------
 arch/powerpc/mm/hugetlbpage.c      |    5 +----
 mm/hugetlb.c                       |    8 +++-----
 3 files changed, 4 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
index 1a4847f67ea8..6f6751d3eba9 100644
--- a/arch/powerpc/include/asm/hugetlb.h
+++ b/arch/powerpc/include/asm/hugetlb.h
@@ -118,12 +118,6 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb, unsigned long addr,
 			    unsigned long ceiling);
 
 /*
- * The version of vma_mmu_pagesize() in arch/powerpc/mm/hugetlbpage.c needs
- * to override the version in mm/hugetlb.c
- */
-#define vma_mmu_pagesize vma_mmu_pagesize
-
-/*
  * If the arch doesn't supply something else, assume that hugepage
  * size aligned regions are ok without further preparation.
  */
diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 876da2bc1796..3a08d211d2ee 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -568,10 +568,7 @@ unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 	if (!radix_enabled())
 		return 1UL << mmu_psize_to_shift(psize);
 #endif
-	if (!is_vm_hugetlb_page(vma))
-		return PAGE_SIZE;
-
-	return huge_page_size(hstate_vma(vma));
+	return vma_kernel_pagesize(vma);
 }
 
 static inline bool is_power_of_4(unsigned long x)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7c204e3d132b..f9c4ea42b04a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -650,15 +650,13 @@ EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 /*
  * Return the page size being used by the MMU to back a VMA. In the majority
  * of cases, the page size used by the kernel matches the MMU size. On
- * architectures where it differs, an architecture-specific version of this
- * function is required.
+ * architectures where it differs, an architecture-specific 'strong'
+ * version of this symbol is required.
  */
-#ifndef vma_mmu_pagesize
-unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
+__weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 {
 	return vma_kernel_pagesize(vma);
 }
-#endif
 
 /*
  * Flags for MAP_PRIVATE reservations.  These are stored in the bottom

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[PATCH v3 2/3] mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct

[Dan Williams]

When device-dax is operating in huge-page mode we want it to behave like
hugetlbfs and report the MMU page mapping size that is being enforced by
the vma. Similar to commit 31383c6865a5 "mm, hugetlbfs: introduce
->split() to vm_operations_struct" it would be messy to teach
vma_mmu_pagesize() about device-dax page mapping sizes in the same
(hstate) way that hugetlbfs communicates this attribute.  Instead, these
patches introduce a new ->pagesize() vm operation.

Reported-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mm.h |    1 +
 mm/hugetlb.c       |   19 +++++++++++--------
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..be0040c9f81b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -383,6 +383,7 @@ struct vm_operations_struct {
 	int (*huge_fault)(struct vm_fault *vmf, enum page_entry_size pe_size);
 	void (*map_pages)(struct vm_fault *vmf,
 			pgoff_t start_pgoff, pgoff_t end_pgoff);
+	unsigned long (*pagesize)(struct vm_area_struct * area);
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f9c4ea42b04a..aaafe5ebaa3e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -636,14 +636,9 @@ EXPORT_SYMBOL_GPL(linear_hugepage_index);
  */
 unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
 {
-	struct hstate *hstate;
-
-	if (!is_vm_hugetlb_page(vma))
-		return PAGE_SIZE;
-
-	hstate = hstate_vma(vma);
-
-	return 1UL << huge_page_shift(hstate);
+	if (vma->vm_ops && vma->vm_ops->pagesize)
+		return vma->vm_ops->pagesize(vma);
+	return PAGE_SIZE;
 }
 EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 
@@ -3150,6 +3145,13 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
 	return 0;
 }
 
+static unsigned long hugetlb_vm_op_pagesize(struct vm_area_struct *vma)
+{
+	struct hstate *hstate = hstate_vma(vma);
+
+	return 1UL << huge_page_shift(hstate);
+}
+
 /*
  * We cannot handle pagefaults against hugetlb pages at all.  They cause
  * handle_mm_fault() to try to instantiate regular-sized pages in the
@@ -3167,6 +3169,7 @@ const struct vm_operations_struct hugetlb_vm_ops = {
 	.open = hugetlb_vm_op_open,
 	.close = hugetlb_vm_op_close,
 	.split = hugetlb_vm_op_split,
+	.pagesize = hugetlb_vm_op_pagesize,
 };
 
 static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,

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[PATCH v3 2/3] mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct

[Dan Williams]

When device-dax is operating in huge-page mode we want it to behave like
hugetlbfs and report the MMU page mapping size that is being enforced by
the vma. Similar to commit 31383c6865a5 "mm, hugetlbfs: introduce
->split() to vm_operations_struct" it would be messy to teach
vma_mmu_pagesize() about device-dax page mapping sizes in the same
(hstate) way that hugetlbfs communicates this attribute.  Instead, these
patches introduce a new ->pagesize() vm operation.

Reported-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mm.h |    1 +
 mm/hugetlb.c       |   19 +++++++++++--------
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..be0040c9f81b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -383,6 +383,7 @@ struct vm_operations_struct {
 	int (*huge_fault)(struct vm_fault *vmf, enum page_entry_size pe_size);
 	void (*map_pages)(struct vm_fault *vmf,
 			pgoff_t start_pgoff, pgoff_t end_pgoff);
+	unsigned long (*pagesize)(struct vm_area_struct * area);
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f9c4ea42b04a..aaafe5ebaa3e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -636,14 +636,9 @@ EXPORT_SYMBOL_GPL(linear_hugepage_index);
  */
 unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
 {
-	struct hstate *hstate;
-
-	if (!is_vm_hugetlb_page(vma))
-		return PAGE_SIZE;
-
-	hstate = hstate_vma(vma);
-
-	return 1UL << huge_page_shift(hstate);
+	if (vma->vm_ops && vma->vm_ops->pagesize)
+		return vma->vm_ops->pagesize(vma);
+	return PAGE_SIZE;
 }
 EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 
@@ -3150,6 +3145,13 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
 	return 0;
 }
 
+static unsigned long hugetlb_vm_op_pagesize(struct vm_area_struct *vma)
+{
+	struct hstate *hstate = hstate_vma(vma);
+
+	return 1UL << huge_page_shift(hstate);
+}
+
 /*
  * We cannot handle pagefaults against hugetlb pages at all.  They cause
  * handle_mm_fault() to try to instantiate regular-sized pages in the
@@ -3167,6 +3169,7 @@ const struct vm_operations_struct hugetlb_vm_ops = {
 	.open = hugetlb_vm_op_open,
 	.close = hugetlb_vm_op_close,
 	.split = hugetlb_vm_op_split,
+	.pagesize = hugetlb_vm_op_pagesize,
 };
 
 static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,

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[PATCH v3 3/3] device-dax: implement ->pagesize() for smaps to report MMUPageSize

[Dan Williams]

Given that device-dax is making similar page mapping size guarantees as
hugetlbfs, emit the size in smaps and any other kernel path that
requests the mapping size of a vma.

Reported-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/dax/device.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 2137dbc29877..0b61f48f21a6 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -439,10 +439,20 @@ static int dev_dax_split(struct vm_area_struct *vma, unsigned long addr)
 	return 0;
 }
 
+static unsigned long dev_dax_pagesize(struct vm_area_struct *vma)
+{
+	struct file *filp = vma->vm_file;
+	struct dev_dax *dev_dax = filp->private_data;
+	struct dax_region *dax_region = dev_dax->region;
+
+	return dax_region->align;
+}
+
 static const struct vm_operations_struct dax_vm_ops = {
 	.fault = dev_dax_fault,
 	.huge_fault = dev_dax_huge_fault,
 	.split = dev_dax_split,
+	.pagesize = dev_dax_pagesize,
 };
 
 static int dax_mmap(struct file *filp, struct vm_area_struct *vma)

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[PATCH v3 3/3] device-dax: implement ->pagesize() for smaps to report MMUPageSize

[Dan Williams]

Given that device-dax is making similar page mapping size guarantees as
hugetlbfs, emit the size in smaps and any other kernel path that
requests the mapping size of a vma.

Reported-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/dax/device.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 2137dbc29877..0b61f48f21a6 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -439,10 +439,20 @@ static int dev_dax_split(struct vm_area_struct *vma, unsigned long addr)
 	return 0;
 }
 
+static unsigned long dev_dax_pagesize(struct vm_area_struct *vma)
+{
+	struct file *filp = vma->vm_file;
+	struct dev_dax *dev_dax = filp->private_data;
+	struct dax_region *dax_region = dev_dax->region;
+
+	return dax_region->align;
+}
+
 static const struct vm_operations_struct dax_vm_ops = {
 	.fault = dev_dax_fault,
 	.huge_fault = dev_dax_huge_fault,
 	.split = dev_dax_split,
+	.pagesize = dev_dax_pagesize,
 };
 
 static int dax_mmap(struct file *filp, struct vm_area_struct *vma)

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Re: [PATCH v3 1/3] mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()

[Michael Ellerman]

Dan Williams <dan.j.williams@intel.com> writes:

> The current powerpc definition of vma_mmu_pagesize() open codes looking
> up the page size via hstate. It is identical to the generic
> vma_kernel_pagesize() implementation.
>
> Now, vma_kernel_pagesize() is growing support for determining the
> page size of Device-DAX vmas in addition to the existing Hugetlbfs page
> size determination.
>
> Ideally, if the powerpc vma_mmu_pagesize() used vma_kernel_pagesize() it
> would automatically benefit from any new vma-type support that is added
> to vma_kernel_pagesize(). However, the powerpc vma_mmu_pagesize() is
> prevented from calling vma_kernel_pagesize() due to a circular header
> dependency that requires vma_mmu_pagesize() to be defined before
> including <linux/hugetlb.h>.
>
> Break this circular dependency by defining the default
> vma_mmu_pagesize() as a __weak symbol to be overridden by the powerpc
> version.
>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  arch/powerpc/include/asm/hugetlb.h |    6 ------
>  arch/powerpc/mm/hugetlbpage.c      |    5 +----
>  mm/hugetlb.c                       |    8 +++-----
>  3 files changed, 4 insertions(+), 15 deletions(-)

This looks OK to me. I was worried switching to a weak symbol would mean
it doesn't get inlined, but it's not inlined today anyway!

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers
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Re: [PATCH v3 1/3] mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()

[Michael Ellerman]

Dan Williams <dan.j.williams@intel.com> writes:

> The current powerpc definition of vma_mmu_pagesize() open codes looking
> up the page size via hstate. It is identical to the generic
> vma_kernel_pagesize() implementation.
>
> Now, vma_kernel_pagesize() is growing support for determining the
> page size of Device-DAX vmas in addition to the existing Hugetlbfs page
> size determination.
>
> Ideally, if the powerpc vma_mmu_pagesize() used vma_kernel_pagesize() it
> would automatically benefit from any new vma-type support that is added
> to vma_kernel_pagesize(). However, the powerpc vma_mmu_pagesize() is
> prevented from calling vma_kernel_pagesize() due to a circular header
> dependency that requires vma_mmu_pagesize() to be defined before
> including <linux/hugetlb.h>.
>
> Break this circular dependency by defining the default
> vma_mmu_pagesize() as a __weak symbol to be overridden by the powerpc
> version.
>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  arch/powerpc/include/asm/hugetlb.h |    6 ------
>  arch/powerpc/mm/hugetlbpage.c      |    5 +----
>  mm/hugetlb.c                       |    8 +++-----
>  3 files changed, 4 insertions(+), 15 deletions(-)

This looks OK to me. I was worried switching to a weak symbol would mean
it doesn't get inlined, but it's not inlined today anyway!

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers

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Re: [PATCH v3 2/3] mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct

[Andrew Morton]

On Thu, 01 Mar 2018 19:49:07 -0800 Dan Williams <dan.j.williams@intel.com> wrote:

> When device-dax is operating in huge-page mode we want it to behave like
> hugetlbfs and report the MMU page mapping size that is being enforced by
> the vma. Similar to commit 31383c6865a5 "mm, hugetlbfs: introduce
> ->split() to vm_operations_struct" it would be messy to teach
> vma_mmu_pagesize() about device-dax page mapping sizes in the same
> (hstate) way that hugetlbfs communicates this attribute.  Instead, these
> patches introduce a new ->pagesize() vm operation.
> 
> ...
>
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -383,6 +383,7 @@ struct vm_operations_struct {
>  	int (*huge_fault)(struct vm_fault *vmf, enum page_entry_size pe_size);
>  	void (*map_pages)(struct vm_fault *vmf,
>  			pgoff_t start_pgoff, pgoff_t end_pgoff);
> +	unsigned long (*pagesize)(struct vm_area_struct * area);

fwiw, vm_operations_struct is documented in
Documentation/filesystems/Locking.  Some bitrotting has occurred :(

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Re: [PATCH v3 2/3] mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct

[Andrew Morton]

On Thu, 01 Mar 2018 19:49:07 -0800 Dan Williams <dan.j.williams@intel.com> wrote:

> When device-dax is operating in huge-page mode we want it to behave like
> hugetlbfs and report the MMU page mapping size that is being enforced by
> the vma. Similar to commit 31383c6865a5 "mm, hugetlbfs: introduce
> ->split() to vm_operations_struct" it would be messy to teach
> vma_mmu_pagesize() about device-dax page mapping sizes in the same
> (hstate) way that hugetlbfs communicates this attribute.  Instead, these
> patches introduce a new ->pagesize() vm operation.
> 
> ...
>
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -383,6 +383,7 @@ struct vm_operations_struct {
>  	int (*huge_fault)(struct vm_fault *vmf, enum page_entry_size pe_size);
>  	void (*map_pages)(struct vm_fault *vmf,
>  			pgoff_t start_pgoff, pgoff_t end_pgoff);
> +	unsigned long (*pagesize)(struct vm_area_struct * area);

fwiw, vm_operations_struct is documented in
Documentation/filesystems/Locking.  Some bitrotting has occurred :(

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