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migration/postcopy: simplify calculation of run_start and fixup_start_addr

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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 <richardw.yang@linux.intel.com>
Message-Id: <20190806004648.8659-2-richardw.yang@linux.intel.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Wei Yang 2019-08-06 08:46:47 +08:00 committed by Dr. David Alan Gilbert
parent 810cf2bbd4
commit dad45ab2be
1 changed files with 7 additions and 27 deletions
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34
migration/ram.c
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@ -2955,7 +2955,6 @@ static void postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
}
while (run_start < pages) {
unsigned long fixup_start_addr;
unsigned long host_offset;
/*
@ -2963,45 +2962,26 @@ 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)) {