mm: smaps*: extend smap_gather_stats to support specified beginning

Extend smap_gather_stats to support indicated beginning address at which
it should start gathering.  To achieve the goal, we add a new parameter
@start assigned by the caller and try to refactor it for simplicity.

If @start is 0, it will use the range of @vma for gathering.
Signed-off-by: Chinwen Chang <chinwen.chang@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Steven Price <steven.price@arm.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Daniel Kiss <daniel.kiss@arm.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jimmy Assarsson <jimmyassarsson@gmail.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: http://lkml.kernel.org/r/1597715898-3854-3-git-send-email-chinwen.chang@mediatek.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/task_mmu.c

@@ -721,9 +721,21 @@ static const struct mm_walk_ops smaps_shmem_walk_ops = {
 	.pte_hole		= smaps_pte_hole,
 };
 
+/*
+ * Gather mem stats from @vma with the indicated beginning
+ * address @start, and keep them in @mss.
+ *
+ * Use vm_start of @vma as the beginning address if @start is 0.
+ */
 static void smap_gather_stats(struct vm_area_struct *vma,
-			     struct mem_size_stats *mss)
+		struct mem_size_stats *mss, unsigned long start)
 {
+	const struct mm_walk_ops *ops = &smaps_walk_ops;
+
+	/* Invalid start */
+	if (start >= vma->vm_end)
+		return;
+
 #ifdef CONFIG_SHMEM
 	/* In case of smaps_rollup, reset the value from previous vma */
 	mss->check_shmem_swap = false;
@@ -740,18 +752,20 @@ static void smap_gather_stats(struct vm_area_struct *vma,
 		 */
 		unsigned long shmem_swapped = shmem_swap_usage(vma);
 
-		if (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
-					!(vma->vm_flags & VM_WRITE)) {
+		if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
+					!(vma->vm_flags & VM_WRITE))) {
 			mss->swap += shmem_swapped;
 		} else {
 			mss->check_shmem_swap = true;
-			walk_page_vma(vma, &smaps_shmem_walk_ops, mss);
-			return;
+			ops = &smaps_shmem_walk_ops;
 		}
 	}
 #endif
 	/* mmap_lock is held in m_start */
-	walk_page_vma(vma, &smaps_walk_ops, mss);
+	if (!start)
+		walk_page_vma(vma, ops, mss);
+	else
+		walk_page_range(vma->vm_mm, start, vma->vm_end, ops, mss);
 }
 
 #define SEQ_PUT_DEC(str, val) \
@@ -803,7 +817,7 @@ static int show_smap(struct seq_file *m, void *v)
 
 	memset(&mss, 0, sizeof(mss));
 
-	smap_gather_stats(vma, &mss);
+	smap_gather_stats(vma, &mss, 0);
 
 	show_map_vma(m, vma);
 
@@ -852,7 +866,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 	hold_task_mempolicy(priv);
 
 	for (vma = priv->mm->mmap; vma; vma = vma->vm_next) {
-		smap_gather_stats(vma, &mss);
+		smap_gather_stats(vma, &mss, 0);
 		last_vma_end = vma->vm_end;
 	}