[PATCH v3] smaps: Report PMD page size for pure PMD mappings

[Andi Kleen <ak@linux.intel.com>]

When a smaps mapping is only PMD mappings report the
PMD page size for MMUPageSize instead of the base page size.

This is a revised version of an earlier patch that tried
to report multiple page sizes, but there were many objections
mainly centered around compatibility for mixed page size
reporting. This patch side steps all of this by
only handling the non mixed case in the simplest possible way.
It also avoids a problem introduced with v2 that page sizes
for mappings with no pages were incorrectly reported.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 fs/proc/task_mmu.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e091931d7ca1..a5c7bc88a539 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1371,6 +1371,7 @@ static int show_smap(struct seq_file *m, void *v)
 {
 	struct vm_area_struct *vma = v;
 	struct mem_size_stats mss = {};
+	unsigned ps;
 
 	smap_gather_stats(vma, &mss, 0);
 
@@ -1378,7 +1379,16 @@ static int show_smap(struct seq_file *m, void *v)
 
 	SEQ_PUT_DEC("Size:           ", vma->vm_end - vma->vm_start);
 	SEQ_PUT_DEC(" kB\nKernelPageSize: ", vma_kernel_pagesize(vma));
-	SEQ_PUT_DEC(" kB\nMMUPageSize:    ", vma_mmu_pagesize(vma));
+	ps = vma_mmu_pagesize(vma);
+	/*
+	 * When the mapping is only PMD THP report the correct page size.
+	 * When multiple pages are there the user has to figure it out
+	 * from other fields.
+	 */
+	if (mss.shmem_thp + mss.file_thp + mss.anonymous_thp == mss.resident &&
+	    mss.resident)
+		ps = HPAGE_PMD_SIZE;
+	SEQ_PUT_DEC(" kB\nMMUPageSize:    ", ps);
 	seq_puts(m, " kB\n");
 
 	__show_smap(m, &mss, false);
-- 
2.53.0