Hi,
On 2021/3/5 22:22, Peter Xu wrote:
Kunkun,
On Fri, Mar 05, 2021 at 03:50:34PM +0800, Kunkun Jiang wrote:
When the host page is a huge page and something is sent in the
current iteration, the migration_rate_limit() should be executed.
If not, this function can be omitted to save time.
Rename tmppages to pages_this_iteration to express its meaning
more clearly.
Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com>
Signed-off-by: Kunkun Jiang <jiangkun...@huawei.com>
---
migration/ram.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index a168da5cdd..9fc5b2997c 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1988,7 +1988,7 @@ static int ram_save_target_page(RAMState *rs,
PageSearchStatus *pss,
static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
bool last_stage)
{
- int tmppages, pages = 0;
+ int pages = 0;
size_t pagesize_bits =
qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS;
unsigned long start_page = pss->page;
@@ -2000,21 +2000,28 @@ static int ram_save_host_page(RAMState *rs,
PageSearchStatus *pss,
}
do {
+ int pages_this_iteration = 0;
+
/* Check if the page is dirty and send it if it is */
if (!migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
pss->page++;
continue;
}
- tmppages = ram_save_target_page(rs, pss, last_stage);
- if (tmppages < 0) {
- return tmppages;
+ pages_this_iteration = ram_save_target_page(rs, pss, last_stage);
+ if (pages_this_iteration < 0) {
+ return pages_this_iteration;
}
- pages += tmppages;
+ pages += pages_this_iteration;
To me, both names are okay, it's just that the new name doesn't really provide
a lot more new information, while it's even longer...
Since you seem to prefer cleaning up tmppages, I'm actually thinking whether
it should be called as "pages" at all since ram_save_target_page() majorly only
returns either 1 if succeeded or <0 if error. There's only one very corner
case of xbzrle where it can return 0 in save_xbzrle_page():
if (encoded_len == 0) {
trace_save_xbzrle_page_skipping();
return 0;
}
I think it means the page didn't change at all, then I'm also wondering maybe
it can also return 1 showing one page migrated (though actually skipped!) which
should still be fine for the callers, e.g., ram_find_and_save_block() who will
finally check this "pages" value.
So I think _maybe_ that's a nicer cleanup to change that "return 0" to "return
1", then another patch to make the return value to be (1) return 0 if page
saved, or (2) return <0 if error. Then here in ram_save_host_page() tmppages
can be renamed to "ret" or "succeed".
Thanks for your advice.
change "return 0" to "return 1" would have a slight effect on
'rs->target_page_count += pages'
in ram_save_iterate(). This may lead to consider more complex
situations. What do you think of
this?
pss->page++;
- /* Allow rate limiting to happen in the middle of huge pages */
- migration_rate_limit();
+ /*
+ * Allow rate limiting to happen in the middle of huge pages if
+ * something is sent in the current iteration.
+ */
+ if (pagesize_bits > 1 && pages_this_iteration > 0) {
+ migration_rate_limit();
+ }
I don't know whether this matters either.. Two calls in there:
migration_update_counters(s, now);
qemu_file_rate_limit(s->to_dst_file);
migration_update_counters() is mostly a noop for 99.9% cases. Looks still
okay...
Thanks,
I think even these two calls shouldn't be called if the host page size
isn't a huge page or
nothing is sent in the current iteration.
Thanks,
Kunkun Jiang
} while ((pss->page & (pagesize_bits - 1)) &&
offset_in_ramblock(pss->block,
((ram_addr_t)pss->page) << TARGET_PAGE_BITS));
--
2.23.0
