[PATCH 3/3] migration/ram: Optimize ram_save_host_page()

[Kunkun Jiang]

Starting from pss->page, ram_save_host_page() will check every page
and send the dirty pages up to the end of the current host page or
the boundary of used_length of the block. If the host page size is
a huge page, the step "check" will take a lot of time.

This will improve performance to use migration_bitmap_find_dirty().

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
---
 migration/ram.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index c7e18dc2fc..c7a2350198 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1994,6 +1994,8 @@ static int ram_save_host_page(RAMState *rs, 
PageSearchStatus *pss,
     int tmppages, pages = 0;
     size_t pagesize_bits =
         qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS;
+    unsigned long hostpage_boundary =
+        QEMU_ALIGN_UP(pss->page + 1, pagesize_bits);
     unsigned long start_page = pss->page;
     int res;
 
@@ -2005,8 +2007,7 @@ static int ram_save_host_page(RAMState *rs, 
PageSearchStatus *pss,
     do {
         /* Check the pages is dirty and if it is send it */
         if (!migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
-            pss->page++;
-            continue;
+            goto find_next;
         }
 
         tmppages = ram_save_target_page(rs, pss, last_stage);
@@ -2015,16 +2016,17 @@ static int ram_save_host_page(RAMState *rs, 
PageSearchStatus *pss,
         }
 
         pages += tmppages;
-        pss->page++;
         /* Allow rate limiting to happen in the middle of huge pages */
         if (pagesize_bits > 1) {
             migration_rate_limit();
         }
-    } while ((pss->page & (pagesize_bits - 1)) &&
+find_next:
+        pss->page = migration_bitmap_find_dirty(rs, pss->block, pss->page);
+    } while ((pss->page < hostpage_boundary) &&
              offset_in_ramblock(pss->block,
                                 ((ram_addr_t)pss->page) << TARGET_PAGE_BITS));
-    /* The offset we leave with is the last one we looked at */
-    pss->page--;
+    /* The offset we leave with is the min boundary of host page and block */
+    pss->page = MIN(pss->page, hostpage_boundary) - 1;
 
     res = ram_save_release_protection(rs, pss, start_page);
     return (res < 0 ? res : pages);
-- 
2.23.0