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[Qemu-devel] [PATCH 1/2] migration/postcopy: simplify calculation of run
From: |
Wei Yang |
Subject: |
[Qemu-devel] [PATCH 1/2] migration/postcopy: simplify calculation of run_start and fixup_start_addr |
Date: |
Tue, 6 Aug 2019 08:46:47 +0800 |
The purpose of the calculation is to find a HostPage which is partially
dirty.
* fixup_start_addr points to the start of the HostPage to discard
* run_start points to the next HostPage to check
While in the middle stage, there would two cases for run_start:
* aligned with HostPage means this is not partially dirty
* not aligned means this is partially dirty
When it is aligned, no work and calculation is necessary. run_start
already points to the start of next HostPage and is ready to continue.
When it is not aligned, the calculation could be simplified with:
* fixup_start_addr = QEMU_ALIGN_DOWN(run_start, host_ratio)
* run_start = QEMU_ALIGN_UP(run_start, host_ratio)
By doing so, run_start always points to the next HostPage to check.
fixup_start_addr always points to the HostPage to discard.
Signed-off-by: Wei Yang <address@hidden>
---
migration/ram.c | 34 +++++++---------------------------
1 file changed, 7 insertions(+), 27 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index c9585487ac..d86661a015 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2956,7 +2956,6 @@ static void postcopy_chunk_hostpages_pass(MigrationState
*ms, bool unsent_pass,
}
while (run_start < pages) {
- unsigned long fixup_start_addr;
unsigned long host_offset;
/*
@@ -2964,45 +2963,26 @@ static void
postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
* page, then we need to fixup this host page.
*/
host_offset = run_start % host_ratio;
- if (host_offset) {
- fixup_start_addr = run_start - host_offset;
- /*
- * This host page has gone, the next loop iteration starts
- * from after the fixup
- */
- run_start = fixup_start_addr + host_ratio;
- } else {
+ if (!host_offset) {
/* Find the end of this run */
- unsigned long run_end;
if (unsent_pass) {
- run_end = find_next_bit(unsentmap, pages, run_start + 1);
+ run_start = find_next_bit(unsentmap, pages, run_start + 1);
} else {
- run_end = find_next_zero_bit(bitmap, pages, run_start + 1);
+ run_start = find_next_zero_bit(bitmap, pages, run_start + 1);
}
/*
* If the end isn't at the start of a host page, then the
* run doesn't finish at the end of a host page
* and we need to discard.
*/
- host_offset = run_end % host_ratio;
- if (host_offset) {
- fixup_start_addr = run_end - host_offset;
- /*
- * This host page has gone, the next loop iteration starts
- * from after the fixup
- */
- run_start = fixup_start_addr + host_ratio;
- } else {
- /*
- * No discards on this iteration, next loop starts from
- * next sent/dirty page
- */
- run_start = run_end + 1;
- }
+ host_offset = run_start % host_ratio;
}
if (host_offset) {
unsigned long page;
+ unsigned long fixup_start_addr = QEMU_ALIGN_DOWN(run_start,
+ host_ratio);
+ run_start = QEMU_ALIGN_UP(run_start, host_ratio);
/* Tell the destination to discard this page */
if (unsent_pass || !test_bit(fixup_start_addr, unsentmap)) {
--
2.17.1