Re: [PATCH -mm] mm, pagemap: Fix swap offset value for PMD migration entry

From: Huang Ying <redacted>

The swap offset reported by /proc/<pid>/pagemap may be not correct for
PMD migration entry.  If addr passed into pagemap_range() isn't
aligned with PMD start address, the swap offset reported doesn't
reflect this.  And in the loop to report information of each sub-page,
the swap offset isn't increased accordingly as that for PFN.

BTW: migration swap entries have PFN information, do we need to
restrict whether to show them?

Signed-off-by: "Huang, Ying" <redacted>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A. Shutemov" <redacted>
Cc: Andrei Vagin <redacted>
Cc: Dan Williams <redacted>
Cc: "Jerome Glisse" <redacted>
Cc: Daniel Colascione <redacted>
Cc: Zi Yan <redacted>
Cc: Naoya Horiguchi <redacted>
---
 fs/proc/task_mmu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 65ae54659833..757e748da613 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c

@@ -1310,9 +1310,11 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 		else if (is_swap_pmd(pmd)) {
 			swp_entry_t entry = pmd_to_swp_entry(pmd);
+			unsigned long offset = swp_offset(entry);
 
+			offset += (addr & ~PMD_MASK) >> PAGE_SHIFT;
 			frame = swp_type(entry) |
-				(swp_offset(entry) << MAX_SWAPFILES_SHIFT);
+				(offset << MAX_SWAPFILES_SHIFT);
 			flags |= PM_SWAP;
 			if (pmd_swp_soft_dirty(pmd))
 				flags |= PM_SOFT_DIRTY;

@@ -1332,6 +1334,8 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 				break;
 			if (pm->show_pfn && (flags & PM_PRESENT))
 				frame++;
+			else if (flags | PM_SWAP)

+				frame += (1 << MAX_SWAPFILES_SHIFT);
 		}
 		spin_unlock(ptl);
 		return err;