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mm: add kdoc comments for vma_start/last_pgoff()

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Describe what vma_start_pgoff() and vma_last_pgoff() actually provide in
detail.

This is in order that we can differentiate this between functions that will
be added in a subsequent patch which provide a different page offset.

We go to lengths to describe the edge cases that can be run into here.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-2-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Liam R. Howlett (Oracle) <liam@infradead.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes
2026-07-10 21:16:43 +01:00
committed by Andrew Morton
parent 995f0eed5e
commit f9711438df
1 changed files with 30 additions and 0 deletions
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30
include/linux/mm.h
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@@ -4311,11 +4311,41 @@ static inline unsigned long vma_pages(const struct vm_area_struct *vma)
return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
}
/**
* vma_start_pgoff() - Get the page offset of the start of @vma
* @vma: The VMA whose page offset is required.
*
* If the VMA is file-backed, this is the page offset into the file.
*
* If @vma is anonymous, this is the virtual page offset of the start of the
* VMA - if unfaulted, then vma->vm_start >> PAGE_SHIFT, if faulted then the
* virtual page offset at the time of first fault.
*
* If @vma is a MAP_PRIVATE file-backed mapping, then this returns the
* page offset within the file.
*
* Edge cases: nommu does not abide by these, MAP_PRIVATE-/dev/zero satisfies
* vma_is_anonymous() but has file-backed page offset, and MAP_PRIVATE-pfnmap
* regions have their page offset set to the first PFN in the range.
*
* Returns: The page offset of the start of @vma.
*/
static inline pgoff_t vma_start_pgoff(const struct vm_area_struct *vma)
{
return vma->vm_pgoff;
}
/**
* vma_last_pgoff() - Get the page offset of the last page in @vma
* @vma: The VMA whose last page offset is required.
*
* This returns the last page offset contained within @vma.
*
* See the description of vma_start_pgoff() for a description of VMA page
* offsets.
*
* Returns: The last page offset of @vma.
*/
static inline pgoff_t vma_last_pgoff(const struct vm_area_struct *vma)
{
return vma_start_pgoff(vma) + vma_pages(vma) - 1;