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Re: [PATCH 1/3] migration/postcopy: not necessary to do discard when can
From: |
Wei Yang |
Subject: |
Re: [PATCH 1/3] migration/postcopy: not necessary to do discard when canonicalizing bitmap |
Date: |
Wed, 25 Sep 2019 08:25:47 +0800 |
User-agent: |
Mutt/1.9.4 (2018-02-28) |
On Tue, Sep 24, 2019 at 11:02:08AM +0100, Dr. David Alan Gilbert wrote:
>* Wei Yang (address@hidden) wrote:
>> All pages, either partially sent or partially dirty, will be discarded in
>> postcopy_send_discard_bm_ram(), since we update the unsentmap to be
>> unsentmap = unsentmap | dirty in ram_postcopy_send_discard_bitmap().
>>
>> This is not necessary to do discard when canonicalizing bitmap. And by
>> doing so, we separate the page discard into two individual steps:
>>
>> * canonicalize bitmap
>> * discard page
>>
>> Signed-off-by: Wei Yang <address@hidden>
>
>Yes, I think when I originally wrote it, the set of pages that was
>discarded was different; I think it was actually the set of
>!unsent & dirty - i.e. only pages that had been sent and then redirtied;
>it later got reworked to include unsent pages as well - so this lot can
>be simplified.
>
>
Thanks for your time :-)
>
>Reviewed-by: Dr. David Alan Gilbert <address@hidden>
>
>> ---
>> migration/ram.c | 14 +-------------
>> 1 file changed, 1 insertion(+), 13 deletions(-)
>>
>> diff --git a/migration/ram.c b/migration/ram.c
>> index 35552c090b..075ddc468c 100644
>> --- a/migration/ram.c
>> +++ b/migration/ram.c
>> @@ -2928,7 +2928,7 @@ static int
>> postcopy_each_ram_send_discard(MigrationState *ms)
>> }
>>
>> /**
>> - * postcopy_chunk_hostpages_pass: canocalize bitmap in hostpages
>> + * postcopy_chunk_hostpages_pass: canonicalize bitmap in hostpages
>> *
>> * Helper for postcopy_chunk_hostpages; it's called twice to
>> * canonicalize the two bitmaps, that are similar, but one is
>> @@ -2991,18 +2991,6 @@ static void
>> postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
>> 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)) {
>> - /* For the unsent_pass we:
>> - * discard partially sent pages
>> - * For the !unsent_pass (dirty) we:
>> - * discard partially dirty pages that were sent
>> - * (any partially sent pages were already discarded
>> - * by the previous unsent_pass)
>> - */
>> - postcopy_discard_send_range(ms, fixup_start_addr,
>> host_ratio);
>> - }
>> -
>> /* Clean up the bitmap */
>> for (page = fixup_start_addr;
>> page < fixup_start_addr + host_ratio; page++) {
>> --
>> 2.17.1
>>
>--
>Dr. David Alan Gilbert / address@hidden / Manchester, UK
--
Wei Yang
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