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migration: Sync requested pages after postcopy recovery

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We synchronize the requested pages right after a postcopy recovery happens.
This helps to synchronize the prioritized pages on source so that the faulted
threads can be served faster.

Reported-by: Xiaohui Li <xiaohli@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201021212721.440373-5-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Peter Xu 2020-10-21 17:27:19 -04:00 committed by Dr. David Alan Gilbert
parent 8f8bfffcf1
commit 0c26781c09
2 changed files with 58 additions and 0 deletions
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57
migration/savevm.c
View File

@ -2010,6 +2010,49 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis)
return LOADVM_QUIT;
}
/* We must be with page_request_mutex held */
static gboolean postcopy_sync_page_req(gpointer key, gpointer value,
gpointer data)
{
MigrationIncomingState *mis = data;
void *host_addr = (void *) key;
ram_addr_t rb_offset;
RAMBlock *rb;
int ret;
rb = qemu_ram_block_from_host(host_addr, true, &rb_offset);
if (!rb) {
/*
* This should _never_ happen. However be nice for a migrating VM to
* not crash/assert. Post an error (note: intended to not use *_once
* because we do want to see all the illegal addresses; and this can
* never be triggered by the guest so we're safe) and move on next.
*/
error_report("%s: illegal host addr %p", __func__, host_addr);
/* Try the next entry */
return FALSE;
}
ret = migrate_send_rp_message_req_pages(mis, rb, rb_offset);
if (ret) {
/* Please refer to above comment. */
error_report("%s: send rp message failed for addr %p",
__func__, host_addr);
return FALSE;
}
trace_postcopy_page_req_sync(host_addr);
return FALSE;
}
static void migrate_send_rp_req_pages_pending(MigrationIncomingState *mis)
{
WITH_QEMU_LOCK_GUARD(&mis->page_request_mutex) {
g_tree_foreach(mis->page_requested, postcopy_sync_page_req, mis);
}
}
static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
{
if (mis->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
@ -2032,6 +2075,20 @@ static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
/* Tell source that "we are ready" */
migrate_send_rp_resume_ack(mis, MIGRATION_RESUME_ACK_VALUE);
/*
* After a postcopy recovery, the source should have lost the postcopy
* queue, or potentially the requested pages could have been lost during
* the network down phase. Let's re-sync with the source VM by re-sending
* all the pending pages that we eagerly need, so these threads won't get
* blocked too long due to the recovery.
*
* Without this procedure, the faulted destination VM threads (waiting for
* page requests right before the postcopy is interrupted) can keep hanging
* until the pages are sent by the source during the background copying of
* pages, or another thread faulted on the same address accidentally.
*/
migrate_send_rp_req_pages_pending(mis);
return 0;
}

1
migration/trace-events
View File

@ -49,6 +49,7 @@ vmstate_save(const char *idstr, const char *vmsd_name) "%s, %s"
vmstate_load(const char *idstr, const char *vmsd_name) "%s, %s"
postcopy_pause_incoming(void) ""
postcopy_pause_incoming_continued(void) ""
postcopy_page_req_sync(void *host_addr) "sync page req %p"
# vmstate.c
vmstate_load_field_error(const char *field, int ret) "field \"%s\" load failed, ret = %d"