[PATCH v4 13/15] virtio-mem: Unplug subblocks right-to-left

[David Hildenbrand]

We unplug blocks right-to-left, let's also unplug subblocks within a block
right-to-left.

Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.li...@gmail.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
 drivers/virtio/virtio_mem.c | 38 ++++++++++++++++---------------------
 1 file changed, 16 insertions(+), 22 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 8dd57b61b09b..a719e1a04ac7 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -353,18 +353,6 @@ static bool virtio_mem_mb_test_sb_unplugged(struct 
virtio_mem *vm,
        return find_next_bit(vm->sb_bitmap, bit + count, bit) >= bit + count;
 }
 
-/*
- * Find the first plugged subblock. Returns vm->nb_sb_per_mb in case there is
- * none.
- */
-static int virtio_mem_mb_first_plugged_sb(struct virtio_mem *vm,
-                                         unsigned long mb_id)
-{
-       const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb;
-
-       return find_next_bit(vm->sb_bitmap, bit + vm->nb_sb_per_mb, bit) - bit;
-}
-
 /*
  * Find the first unplugged subblock. Returns vm->nb_sb_per_mb in case there is
  * none.
@@ -1016,21 +1004,27 @@ static int virtio_mem_mb_unplug_any_sb(struct 
virtio_mem *vm,
        int sb_id, count;
        int rc;
 
+       sb_id = vm->nb_sb_per_mb - 1;
        while (*nb_sb) {
-               sb_id = virtio_mem_mb_first_plugged_sb(vm, mb_id);
-               if (sb_id >= vm->nb_sb_per_mb)
+               /* Find the next candidate subblock */
+               while (sb_id >= 0 &&
+                      virtio_mem_mb_test_sb_unplugged(vm, mb_id, sb_id, 1))
+                       sb_id--;
+               if (sb_id < 0)
                        break;
+               /* Try to unplug multiple subblocks at a time */
                count = 1;
-               while (count < *nb_sb &&
-                      sb_id + count  < vm->nb_sb_per_mb &&
-                      virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id + count,
-                                                    1))
+               while (count < *nb_sb && sb_id > 0 &&
+                      virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id - 1, 1)) {
                        count++;
+                       sb_id--;
+               }
 
                rc = virtio_mem_mb_unplug_sb(vm, mb_id, sb_id, count);
                if (rc)
                        return rc;
                *nb_sb -= count;
+               sb_id--;
        }
 
        return 0;
@@ -1337,12 +1331,12 @@ static int virtio_mem_mb_unplug_any_sb_online(struct 
virtio_mem *vm,
         * we should sense via something like is_mem_section_removable()
         * first if it makes sense to go ahead any try to allocate.
         */
-       for (sb_id = 0; sb_id < vm->nb_sb_per_mb && *nb_sb; sb_id++) {
+       for (sb_id = vm->nb_sb_per_mb - 1; sb_id >= 0 && *nb_sb; sb_id--) {
                /* Find the next candidate subblock */
-               while (sb_id < vm->nb_sb_per_mb &&
+               while (sb_id >= 0 &&
                       !virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
-                       sb_id++;
-               if (sb_id >= vm->nb_sb_per_mb)
+                       sb_id--;
+               if (sb_id < 0)
                        break;
 
                start_pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
-- 
2.25.3