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Re: [PATCH 1/3] migration/postcopy: not necessary to do discard when can
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH 1/3] migration/postcopy: not necessary to do discard when canonicalizing bitmap |
Date: |
Tue, 24 Sep 2019 11:02:08 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* 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.
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
- Re: [PATCH 1/3] migration/postcopy: not necessary to do discard when canonicalizing bitmap,
Dr. David Alan Gilbert <=