It's often useful to obtain the number of pages a given address lies at within a VMA.
Add linear_page_delta() to determine this and update linear_page_index() to make use of it. Add comments to describe both linear_page_delta() and linear_page_index(). No functional change intended. Signed-off-by: Lorenzo Stoakes <[email protected]> --- include/linux/pagemap.h | 37 +++++++++++++++++++++++++++++++++++-- 1 file changed, 35 insertions(+), 2 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 2c3718d592d6..644c0f25ae73 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1063,11 +1063,44 @@ static inline pgoff_t folio_pgoff(const struct folio *folio) return folio->index; } +/** + * linear_page_delta() - Determine the relative page offset of @address within + * @vma. + * @vma: The VMA in which @address resides. + * @address: The address whose relative page offset is required. + * + * The result is identical for both file-backed and anonymous mappings and + * simply determines how many pages @address lies from @vma->vm_start. + * + * Returns: The number of pages @address is offset by within @vma. + */ +static inline pgoff_t linear_page_delta(const struct vm_area_struct *vma, + const unsigned long address) +{ + return (address - vma->vm_start) >> PAGE_SHIFT; +} + +/** + * linear_page_index() - Determine the absolute page offset of @address within + * @vma. + * @vma: The VMA in which @address resides. + * @address: The address whose absolute page offset is required. + * + * For file-backed mappings, this returns the page offset of @address within the + * file. + * + * For anonymous mappings, this returns the virtual page offset of @address, + * which is the page offset the address possessed at the time the VMA was first + * faulted. + * + * Returns: The absolute page offset of @address within @vma. + */ static inline pgoff_t linear_page_index(const struct vm_area_struct *vma, const unsigned long address) { pgoff_t pgoff; - pgoff = (address - vma->vm_start) >> PAGE_SHIFT; + + pgoff = linear_page_delta(vma, address); pgoff += vma->vm_pgoff; return pgoff; } @@ -1219,7 +1252,7 @@ static inline vm_fault_t folio_lock_or_retry(struct folio *folio, void folio_wait_bit(struct folio *folio, int bit_nr); int folio_wait_bit_killable(struct folio *folio, int bit_nr); -/* +/* * Wait for a folio to be unlocked. * * This must be called with the caller "holding" the folio, -- 2.54.0
