Don't take the bitmap mutex when sending pages, or when being throttled by
migration_rate_limit() (which is a bit tricky to call it here in ram code,
but seems still helpful).
It prepares for the possibility of concurrently sending pages in >1 threads
using the function ram_save_host_page() because all threads may need the
bitmap_mutex to operate on bitmaps, so that either sendmsg() or any kind of
qemu_sem_wait() blocking for one thread will not block the other from
progressing.
Signed-off-by: Peter Xu <pet...@redhat.com>
---
migration/ram.c | 41 ++++++++++++++++++++++++++++++-----------
1 file changed, 30 insertions(+), 11 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index b9ac2d6921..578ad8d70a 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2462,6 +2462,7 @@ static void postcopy_preempt_reset_channel(RAMState *rs)
*/
static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
{
+ bool page_dirty, preempt_active = postcopy_preempt_active();
int tmppages, pages = 0;
size_t pagesize_bits =
qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS;
@@ -2485,22 +2486,40 @@ static int ram_save_host_page(RAMState *rs,
PageSearchStatus *pss)
break;
}
- /* Check the pages is dirty and if it is send it */
- if (migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
- tmppages = ram_save_target_page(rs, pss);
- if (tmppages < 0) {
- return tmppages;
- }
+ page_dirty = migration_bitmap_clear_dirty(rs, pss->block, pss->page);
- pages += tmppages;
+ /* Check the pages is dirty and if it is send it */
+ if (page_dirty) {
/*
- * Allow rate limiting to happen in the middle of huge pages if
- * something is sent in the current iteration.
+ * Properly yield the lock only in postcopy preempt mode
+ * because both migration thread and rp-return thread can
+ * operate on the bitmaps.
*/
- if (pagesize_bits > 1 && tmppages > 0) {
- migration_rate_limit();
+ if (preempt_active) {
+ qemu_mutex_unlock(&rs->bitmap_mutex);
+ }
+ tmppages = ram_save_target_page(rs, pss);
+ if (tmppages >= 0) {
+ pages += tmppages;
+ /*
+ * Allow rate limiting to happen in the middle of huge pages if
+ * something is sent in the current iteration.
+ */
+ if (pagesize_bits > 1 && tmppages > 0) {
+ migration_rate_limit();
+ }
}
+ if (preempt_active) {
+ qemu_mutex_lock(&rs->bitmap_mutex);
+ }
+ } else {
+ tmppages = 0;
}
+
+ if (tmppages < 0) {
+ return tmppages;
+ }
+
pss->page = migration_bitmap_find_dirty(rs, pss->block, pss->page);
} while ((pss->page < hostpage_boundary) &&
offset_in_ramblock(pss->block,
--
2.37.3
