X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=mm%2Fswapfile.c;h=58877312cf6b94b74da00b8913bf8db64d56ab26;hb=b4a237598aa740562f842db76d97465c44fb74c1;hp=aebc2dd6e64975e2589429a0e22929f96c4d7532;hpb=752240e74d650faa24425adc523f1308973ea51c;p=firefly-linux-kernel-4.4.55.git

diff --git a/mm/swapfile.c b/mm/swapfile.c
index aebc2dd6e649..58877312cf6b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -874,6 +874,48 @@ int page_swapcount(struct page *page)
 	return count;
 }
 
+/*
+ * How many references to @entry are currently swapped out?
+ * This considers COUNT_CONTINUED so it returns exact answer.
+ */
+int swp_swapcount(swp_entry_t entry)
+{
+	int count, tmp_count, n;
+	struct swap_info_struct *p;
+	struct page *page;
+	pgoff_t offset;
+	unsigned char *map;
+
+	p = swap_info_get(entry);
+	if (!p)
+		return 0;
+
+	count = swap_count(p->swap_map[swp_offset(entry)]);
+	if (!(count & COUNT_CONTINUED))
+		goto out;
+
+	count &= ~COUNT_CONTINUED;
+	n = SWAP_MAP_MAX + 1;
+
+	offset = swp_offset(entry);
+	page = vmalloc_to_page(p->swap_map + offset);
+	offset &= ~PAGE_MASK;
+	VM_BUG_ON(page_private(page) != SWP_CONTINUED);
+
+	do {
+		page = list_entry(page->lru.next, struct page, lru);
+		map = kmap_atomic(page);
+		tmp_count = map[offset];
+		kunmap_atomic(map);
+
+		count += (tmp_count & ~COUNT_CONTINUED) * n;
+		n *= (SWAP_CONT_MAX + 1);
+	} while (tmp_count & COUNT_CONTINUED);
+out:
+	spin_unlock(&p->lock);
+	return count;
+}
+
 /*
  * We can write to an anon page without COW if there are no other references
  * to it.  And as a side-effect, free up its swap: because the old content