[PATCH] smaps: Report correct page sizes with THP

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

Recently I wasted quite some time debugging why THP didn't work, when it
was just smaps always reporting the base page size. It has separate
counts for (non m) THP, but using them is not always obvious. For
standard THP the page sizes can be actually derived from the existing
counts, so do just do that. I left KernelPageSize alone.
The mixed page size case is reported with a new MMUPageSize2 item.
This doesn't do anything about mTHP reporting, but even the basic
smaps is not aware of it so far.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 Documentation/filesystems/proc.rst |  2 +-
 fs/proc/task_mmu.c                 | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 8256e857e2d7..7c776046d15a 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -483,7 +483,7 @@ entries; the page size used by the MMU when backing a VMA (in most cases,
 the same as KernelPageSize); the amount of the mapping that is currently
 resident in RAM (RSS); the process's proportional share of this mapping
 (PSS); and the number of clean and dirty shared and private pages in the
-mapping.
+mapping. If the mapping has multiple page size there might be a MMUPageSize2.
 
 The "proportional set size" (PSS) of a process is the count of pages it has
 in memory, where each page is divided by the number of processes sharing it.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 26188a4ad1ab..9123e59dcf4c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1377,7 +1377,19 @@ 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));
+
+	/* Only THP? */
+	if (mss.shmem_thp + mss.file_thp + mss.anonymous_thp == mss.resident &&
+	    mss.resident > 0) {
+		SEQ_PUT_DEC(" kB\nMMUPageSize:    ", HPAGE_PMD_SIZE);
+	} else {
+		unsigned ps = vma_mmu_pagesize(vma);
+		/* Will need adjustments when more THP page sizes are added. */
+		SEQ_PUT_DEC(" kB\nMMUPageSize:    ", ps);
+		if (mss.shmem_thp + mss.file_thp + mss.anonymous_thp > 0 &&
+		    ps != HPAGE_PMD_SIZE)
+			SEQ_PUT_DEC(" kB\nMMUPageSize2:   ", HPAGE_PMD_SIZE);
+	}
 	seq_puts(m, " kB\n");
 
 	__show_smap(m, &mss, false);
-- 
2.52.0