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migration/ram: avoid to do log clear in the last round

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There won't be any ram sync after the stage of save_complete, therefore
it's unnecessary to do manually protect for dirty pages being sent. Skip
to do this in last round can reduce noticeable downtime.

Signed-off-by: Yanfei Xu <yanfei.xu@bytedance.com>
Tested-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20250514115827.3216082-1-yanfei.xu@bytedance.com
[peterx: add comments]
Signed-off-by: Peter Xu <peterx@redhat.com>
This commit is contained in:
Yanfei Xu
2025-06-23 16:03:59 -04:00
committed by Peter Xu
parent 43ba160cb4
commit fd0377150d
1 changed files with 15 additions and 7 deletions
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migration/ram.c
+15 -7
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@@ -831,14 +831,22 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs,
bool ret;
/*
* Clear dirty bitmap if needed. This _must_ be called before we
* send any of the page in the chunk because we need to make sure
* we can capture further page content changes when we sync dirty
* log the next time. So as long as we are going to send any of
* the page in the chunk we clear the remote dirty bitmap for all.
* Clearing it earlier won't be a problem, but too late will.
* During the last stage (after source VM stopped), resetting the write
* protections isn't needed as we know there will be either (1) no
* further writes if migration will complete, or (2) migration fails
* at last then tracking isn't needed either.
*/
migration_clear_memory_region_dirty_bitmap(rb, page);
if (!rs->last_stage) {
/*
* Clear dirty bitmap if needed. This _must_ be called before we
* send any of the page in the chunk because we need to make sure
* we can capture further page content changes when we sync dirty
* log the next time. So as long as we are going to send any of
* the page in the chunk we clear the remote dirty bitmap for all.
* Clearing it earlier won't be a problem, but too late will.
*/
migration_clear_memory_region_dirty_bitmap(rb, page);
}
ret = test_and_clear_bit(page, rb->bmap);
if (ret) {