The bulk stage is kind of weird: migration_bitmap_find_dirty() will
indicate a dirty page, however, ram_save_host_page() will never save it, as
migration_bitmap_clear_dirty() detects that it is not dirty.
We already fill the bitmap in ram_list_init_bitmaps() with ones, marking
everything dirty - it didn't used to be that way, which is why we needed
an explicit first bulk stage.
Let's simplify: make the bitmap the single source of thuth. Explicitly
handle the "xbzrle_enabled after first round" case.
Regarding XBZRLE (implicitly handled via "ram_bulk_stage = false" right
now), there is now a slight change in behavior:
- Colo: When starting, it will be disabled (was implicitly enabled)
until the first round actually finishes.
- Free page hinting: When starting, XBZRLE will be disabled (was implicitly
enabled) until the first round actually finished.
- Snapshots: When starting, XBZRLE will be disabled. We essentially only
do a single run, so I guess it will never actually get disabled.
Postcopy seems to indirectly disable it in ram_save_page(), so there
shouldn't be really any change.
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
Our dirty bitmap handling is right now a little confusing due to the bulk
stage. Am i missing something important? Can someone comment on the
expected XBZRLE handling? It all is a little bit too intertwined for my
taste.
---
hw/virtio/virtio-balloon.c | 4 +-
hw/virtio/virtio-mem.c | 3 --
include/migration/misc.h | 1 -
migration/ram.c | 78 +++++++++-----------------------------
4 files changed, 18 insertions(+), 68 deletions(-)
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index e770955176..d162b89603 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -659,9 +659,6 @@ virtio_balloon_free_page_hint_notify(NotifierWithReturn *n,
void *data)
}
switch (pnd->reason) {
- case PRECOPY_NOTIFY_SETUP:
- precopy_enable_free_page_optimization();
- break;
case PRECOPY_NOTIFY_BEFORE_BITMAP_SYNC:
virtio_balloon_free_page_stop(dev);
break;
@@ -681,6 +678,7 @@ virtio_balloon_free_page_hint_notify(NotifierWithReturn *n,
void *data)
*/
virtio_balloon_free_page_done(dev);
break;
+ case PRECOPY_NOTIFY_SETUP:
case PRECOPY_NOTIFY_COMPLETE:
break;
default:
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 99d0712195..c7d261ffe7 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -1063,9 +1063,6 @@ static int virtio_mem_precopy_notify(NotifierWithReturn
*n, void *data)
PrecopyNotifyData *pnd = data;
switch (pnd->reason) {
- case PRECOPY_NOTIFY_SETUP:
- precopy_enable_free_page_optimization();
- break;
case PRECOPY_NOTIFY_AFTER_BITMAP_SYNC:
virtio_mem_precopy_exclude_unplugged(vmem);
break;
diff --git a/include/migration/misc.h b/include/migration/misc.h
index bccc1b6b44..69c7e7e14b 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -37,7 +37,6 @@ void precopy_infrastructure_init(void);
void precopy_add_notifier(NotifierWithReturn *n);
void precopy_remove_notifier(NotifierWithReturn *n);
int precopy_notify(PrecopyNotifyReason reason, Error **errp);
-void precopy_enable_free_page_optimization(void);
void ram_mig_init(void);
void qemu_guest_free_page_hint(void *addr, size_t len);
diff --git a/migration/ram.c b/migration/ram.c
index 72143da0ac..7394a9c414 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -313,10 +313,6 @@ struct RAMState {
ram_addr_t last_page;
/* last ram version we have seen */
uint32_t last_version;
- /* We are in the first round */
- bool ram_bulk_stage;
- /* The free page optimization is enabled */
- bool fpo_enabled;
/* How many times we have dirty too many pages */
int dirty_rate_high_cnt;
/* these variables are used for bitmap sync */
@@ -332,6 +328,8 @@ struct RAMState {
uint64_t xbzrle_pages_prev;
/* Amount of xbzrle encoded bytes since the beginning of the period */
uint64_t xbzrle_bytes_prev;
+ /* Start using XBZRLE (e.g., after the first round). */
+ bool xbzrle_enabled;
/* compression statistics since the beginning of the period */
/* amount of count that no free thread to compress data */
@@ -385,15 +383,6 @@ int precopy_notify(PrecopyNotifyReason reason, Error
**errp)
return notifier_with_return_list_notify(&precopy_notifier_list, &pnd);
}
-void precopy_enable_free_page_optimization(void)
-{
- if (!ram_state) {
- return;
- }
-
- ram_state->fpo_enabled = true;
-}
-
uint64_t ram_bytes_remaining(void)
{
return ram_state ? (ram_state->migration_dirty_pages * TARGET_PAGE_SIZE) :
@@ -666,7 +655,7 @@ static void mig_throttle_guest_down(uint64_t
bytes_dirty_period,
*/
static void xbzrle_cache_zero_page(RAMState *rs, ram_addr_t current_addr)
{
- if (rs->ram_bulk_stage || !migrate_use_xbzrle()) {
+ if (!rs->xbzrle_enabled) {
return;
}
@@ -794,23 +783,12 @@ unsigned long migration_bitmap_find_dirty(RAMState *rs, RAMBlock *rb,
{
unsigned long size = rb->used_length >> TARGET_PAGE_BITS;
unsigned long *bitmap = rb->bmap;
- unsigned long next;
if (ramblock_is_ignored(rb)) {
return size;
}
- /*
- * When the free page optimization is enabled, we need to check the bitmap
- * to send the non-free pages rather than all the pages in the bulk stage.
- */
- if (!rs->fpo_enabled && rs->ram_bulk_stage && start > 0) {
- next = start + 1;
- } else {
- next = find_next_bit(bitmap, size, start);
- }
-
- return next;
+ return find_next_bit(bitmap, size, start);
}
static inline bool migration_bitmap_clear_dirty(RAMState *rs,
@@ -1188,8 +1166,7 @@ static int ram_save_page(RAMState *rs, PageSearchStatus
*pss, bool last_stage)
trace_ram_save_page(block->idstr, (uint64_t)offset, p);
XBZRLE_cache_lock();
- if (!rs->ram_bulk_stage && !migration_in_postcopy() &&
- migrate_use_xbzrle()) {
+ if (rs->xbzrle_enabled && !migration_in_postcopy()) {
pages = save_xbzrle_page(rs, &p, current_addr, block,
offset, last_stage);
if (!last_stage) {
@@ -1389,7 +1366,10 @@ static bool find_dirty_block(RAMState *rs,
PageSearchStatus *pss, bool *again)
pss->block = QLIST_FIRST_RCU(&ram_list.blocks);
/* Flag that we've looped */
pss->complete_round = true;
- rs->ram_bulk_stage = false;
+ /* After the first round, enable XBZRLE. */
+ if (migrate_use_xbzrle()) {
+ rs->xbzrle_enabled = true;
+ }
}
/* Didn't find anything this time, but try again on the new block */
*again = true;
@@ -1752,14 +1732,6 @@ static bool get_queued_page(RAMState *rs,
PageSearchStatus *pss)
}
if (block) {
- /*
- * As soon as we start servicing pages out of order, then we have
- * to kill the bulk stage, since the bulk stage assumes
- * in (migration_bitmap_find_and_reset_dirty) that every page is
- * dirty, that's no longer true.
- */
- rs->ram_bulk_stage = false;
-
/*
* We want the background search to continue from the queued page
* since the guest is likely to want other pages near to the page
@@ -1872,15 +1844,15 @@ static bool save_page_use_compression(RAMState *rs)
}
/*
- * If xbzrle is on, stop using the data compression after first
- * round of migration even if compression is enabled. In theory,
- * xbzrle can do better than compression.
+ * If xbzrle is enabled (e.g., after first round of migration), stop
+ * using the data compression. In theory, xbzrle can do better than
+ * compression.
*/
- if (rs->ram_bulk_stage || !migrate_use_xbzrle()) {
- return true;
+ if (rs->xbzrle_enabled) {
+ return false;
}
- return false;
+ return true;
}
/*
@@ -2187,8 +2159,7 @@ static void ram_state_reset(RAMState *rs)
rs->last_sent_block = NULL;
rs->last_page = 0;
rs->last_version = ram_list.version;
- rs->ram_bulk_stage = true;
- rs->fpo_enabled = false;
+ rs->xbzrle_enabled = false;
}
#define MAX_WAIT 50 /* ms, half buffered_file limit */
@@ -2672,15 +2643,7 @@ static void ram_state_resume_prepare(RAMState *rs,
QEMUFile *out)
/* This may not be aligned with current bitmaps. Recalculate. */
rs->migration_dirty_pages = pages;
- rs->last_seen_block = NULL;
- rs->last_sent_block = NULL;
- rs->last_page = 0;
- rs->last_version = ram_list.version;
- /*
- * Disable the bulk stage, otherwise we'll resend the whole RAM no
- * matter what we have sent.
- */
- rs->ram_bulk_stage = false;
+ ram_state_reset(rs);
/* Update RAMState cache of output QEMUFile */
rs->f = out;
@@ -3298,16 +3261,9 @@ static void decompress_data_with_multi_threads(QEMUFile
*f,
qemu_mutex_unlock(&decomp_done_lock);
}
- /*
- * we must set ram_bulk_stage to false, otherwise in
- * migation_bitmap_find_dirty the bitmap will be unused and
- * all the pages in ram cache wil be flushed to the ram of
- * secondary VM.
- */
static void colo_init_ram_state(void)
{
ram_state_init(&ram_state);
- ram_state->ram_bulk_stage = false;
}
/*