2 files changed, 55 insertions, 1 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 9f13b6e28676..fdeb5b33349f 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -460,7 +460,10 @@ and a page is modified, the file page is replaced by a private anonymous copy.
 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
-"SwapPss" shows proportional swap share of this mapping.
+For shmem mappings, "Swap" includes also the size of the mapped (and not
+replaced by copy-on-write) part of the underlying shmem object out on swap.
+"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
+does not take into account swapped out page of underlying shmem objects.
 "Locked" indicates whether the mapping is locked in memory or not.
 
 "VmFlags" field deserves a separate description. This member represents the kernel
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 187b3b5f242e..85ef60fdf2c0 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -451,6 +451,7 @@ struct mem_size_stats {
         unsigned long private_hugetlb;
         u64 pss;
         u64 swap_pss;
+        bool check_shmem_swap;
 };
 
 static void smaps_account(struct mem_size_stats *mss, struct page *page,
@@ -485,6 +486,45 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
         }
 }
 
+#ifdef CONFIG_SHMEM
+static unsigned long smaps_shmem_swap(struct vm_area_struct *vma,
+                unsigned long addr)
+{
+        struct page *page;
+
+        page = find_get_entry(vma->vm_file->f_mapping,
+                                        linear_page_index(vma, addr));
+        if (!page)
+                return 0;
+
+        if (radix_tree_exceptional_entry(page))
+                return PAGE_SIZE;
+
+        page_cache_release(page);
+        return 0;
+
+}
+
+static int smaps_pte_hole(unsigned long addr, unsigned long end,
+                struct mm_walk *walk)
+{
+        struct mem_size_stats *mss = walk->private;
+
+        while (addr < end) {
+                mss->swap += smaps_shmem_swap(walk->vma, addr);
+                addr += PAGE_SIZE;
+        }
+
+        return 0;
+}
+#else
+static unsigned long smaps_shmem_swap(struct vm_area_struct *vma,
+                unsigned long addr)
+{
+        return 0;
+}
+#endif
+
 static void smaps_pte_entry(pte_t *pte, unsigned long addr,
                 struct mm_walk *walk)
 {
@@ -512,6 +552,9 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
                         }
                 } else if (is_migration_entry(swpent))
                         page = migration_entry_to_page(swpent);
+        } else if (unlikely(IS_ENABLED(CONFIG_SHMEM) && mss->check_shmem_swap
+                                                        && pte_none(*pte))) {
+                mss->swap += smaps_shmem_swap(vma, addr);
         }
 
         if (!page)
@@ -671,6 +714,14 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
         };
 
         memset(&mss, 0, sizeof mss);
+
+#ifdef CONFIG_SHMEM
+        if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) {
+                mss.check_shmem_swap = true;
+                smaps_walk.pte_hole = smaps_pte_hole;
+        }
+#endif
+
         /* mmap_sem is held in m_start */
         walk_page_vma(vma, &smaps_walk);