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Re: [PATCH 2/3] migration/postcopy: unsentmap is not necessary for postc
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH 2/3] migration/postcopy: unsentmap is not necessary for postcopy |
Date: |
Tue, 24 Sep 2019 11:18:37 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* Wei Yang (address@hidden) wrote:
> Commit f3f491fcd6dd594ba695 ('Postcopy: Maintain unsentmap') introduced
> unsentmap to track not yet sent pages.
>
> This is not necessary since:
>
> * unsentmap is a sub-set of bmap before postcopy start
> * unsentmap is the summation of bmap and unsentmap after canonicalizing
>
> This patch just removes it.
>
> Signed-off-by: Wei Yang <address@hidden>
Yes, that's simpler
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> ---
> include/exec/ram_addr.h | 6 ----
> migration/ram.c | 80 ++++++++---------------------------------
> 2 files changed, 14 insertions(+), 72 deletions(-)
>
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index a327a80cfe..e96e621de5 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -44,12 +44,6 @@ struct RAMBlock {
> size_t page_size;
> /* dirty bitmap used during migration */
> unsigned long *bmap;
> - /* bitmap of pages that haven't been sent even once
> - * only maintained and used in postcopy at the moment
> - * where it's used to send the dirtymap at the start
> - * of the postcopy phase
> - */
> - unsigned long *unsentmap;
> /* bitmap of already received pages in postcopy */
> unsigned long *receivedmap;
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 075ddc468c..066eb4755f 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2348,7 +2348,7 @@ static bool get_queued_page(RAMState *rs,
> PageSearchStatus *pss)
> dirty = test_bit(page, block->bmap);
> if (!dirty) {
> trace_get_queued_page_not_dirty(block->idstr,
> (uint64_t)offset,
> - page, test_bit(page, block->unsentmap));
> + page, test_bit(page, block->bmap));
We could actually lose that last trace parameter.
Dave
> } else {
> trace_get_queued_page(block->idstr, (uint64_t)offset, page);
> }
> @@ -2619,10 +2619,6 @@ static int ram_save_host_page(RAMState *rs,
> PageSearchStatus *pss,
> }
>
> pages += tmppages;
> - if (pss->block->unsentmap) {
> - clear_bit(pss->page, pss->block->unsentmap);
> - }
> -
> pss->page++;
> } while ((pss->page & (pagesize_bits - 1)) &&
> offset_in_ramblock(pss->block, pss->page << TARGET_PAGE_BITS));
> @@ -2776,8 +2772,6 @@ static void ram_save_cleanup(void *opaque)
> block->clear_bmap = NULL;
> g_free(block->bmap);
> block->bmap = NULL;
> - g_free(block->unsentmap);
> - block->unsentmap = NULL;
> }
>
> xbzrle_cleanup();
> @@ -2857,8 +2851,6 @@ void
> ram_postcopy_migrated_memory_release(MigrationState *ms)
> * Returns zero on success
> *
> * Callback from postcopy_each_ram_send_discard for each RAMBlock
> - * Note: At this point the 'unsentmap' is the processed bitmap combined
> - * with the dirtymap; so a '1' means it's either dirty or unsent.
> *
> * @ms: current migration state
> * @block: RAMBlock to discard
> @@ -2867,17 +2859,17 @@ static int
> postcopy_send_discard_bm_ram(MigrationState *ms, RAMBlock *block)
> {
> unsigned long end = block->used_length >> TARGET_PAGE_BITS;
> unsigned long current;
> - unsigned long *unsentmap = block->unsentmap;
> + unsigned long *bitmap = block->bmap;
>
> for (current = 0; current < end; ) {
> - unsigned long one = find_next_bit(unsentmap, end, current);
> + unsigned long one = find_next_bit(bitmap, end, current);
> unsigned long zero, discard_length;
>
> if (one >= end) {
> break;
> }
>
> - zero = find_next_zero_bit(unsentmap, end, one + 1);
> + zero = find_next_zero_bit(bitmap, end, one + 1);
>
> if (zero >= end) {
> discard_length = end - one;
> @@ -2938,16 +2930,12 @@ static int
> postcopy_each_ram_send_discard(MigrationState *ms)
> * clean, not a mix. This function canonicalizes the bitmaps.
> *
> * @ms: current migration state
> - * @unsent_pass: if true we need to canonicalize partially unsent host pages
> - * otherwise we need to canonicalize partially dirty host pages
> * @block: block that contains the page we want to canonicalize
> */
> -static void postcopy_chunk_hostpages_pass(MigrationState *ms, bool
> unsent_pass,
> - RAMBlock *block)
> +static void postcopy_chunk_hostpages_pass(MigrationState *ms, RAMBlock
> *block)
> {
> RAMState *rs = ram_state;
> unsigned long *bitmap = block->bmap;
> - unsigned long *unsentmap = block->unsentmap;
> unsigned int host_ratio = block->page_size / TARGET_PAGE_SIZE;
> unsigned long pages = block->used_length >> TARGET_PAGE_BITS;
> unsigned long run_start;
> @@ -2957,13 +2945,8 @@ static void
> postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
> return;
> }
>
> - if (unsent_pass) {
> - /* Find a sent page */
> - run_start = find_next_zero_bit(unsentmap, pages, 0);
> - } else {
> - /* Find a dirty page */
> - run_start = find_next_bit(bitmap, pages, 0);
> - }
> + /* Find a dirty page */
> + run_start = find_next_bit(bitmap, pages, 0);
>
> while (run_start < pages) {
>
> @@ -2973,11 +2956,7 @@ static void
> postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
> */
> if (QEMU_IS_ALIGNED(run_start, host_ratio)) {
> /* Find the end of this run */
> - if (unsent_pass) {
> - run_start = find_next_bit(unsentmap, pages, run_start + 1);
> - } else {
> - run_start = 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
> @@ -2994,9 +2973,6 @@ static void
> postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
> /* Clean up the bitmap */
> for (page = fixup_start_addr;
> page < fixup_start_addr + host_ratio; page++) {
> - /* All pages in this host page are now not sent */
> - set_bit(page, unsentmap);
> -
> /*
> * Remark them as dirty, updating the count for any pages
> * that weren't previously dirty.
> @@ -3005,13 +2981,8 @@ static void
> postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
> }
> }
>
> - if (unsent_pass) {
> - /* Find the next sent page for the next iteration */
> - run_start = find_next_zero_bit(unsentmap, pages, run_start);
> - } else {
> - /* Find the next dirty page for the next iteration */
> - run_start = find_next_bit(bitmap, pages, run_start);
> - }
> + /* Find the next dirty page for the next iteration */
> + run_start = find_next_bit(bitmap, pages, run_start);
> }
> }
>
> @@ -3033,13 +3004,10 @@ static int postcopy_chunk_hostpages(MigrationState
> *ms, RAMBlock *block)
> {
> postcopy_discard_send_init(ms, block->idstr);
>
> - /* First pass: Discard all partially sent host pages */
> - postcopy_chunk_hostpages_pass(ms, true, block);
> /*
> - * Second pass: Ensure that all partially dirty host pages are made
> - * fully dirty.
> + * Ensure that all partially dirty host pages are made fully dirty.
> */
> - postcopy_chunk_hostpages_pass(ms, false, block);
> + postcopy_chunk_hostpages_pass(ms, block);
>
> postcopy_discard_send_finish(ms);
> return 0;
> @@ -3077,19 +3045,6 @@ int ram_postcopy_send_discard_bitmap(MigrationState
> *ms)
> rs->last_page = 0;
>
> RAMBLOCK_FOREACH_NOT_IGNORED(block) {
> - unsigned long pages = block->used_length >> TARGET_PAGE_BITS;
> - unsigned long *bitmap = block->bmap;
> - unsigned long *unsentmap = block->unsentmap;
> -
> - if (!unsentmap) {
> - /* We don't have a safe way to resize the sentmap, so
> - * if the bitmap was resized it will be NULL at this
> - * point.
> - */
> - error_report("migration ram resized during precopy phase");
> - rcu_read_unlock();
> - return -EINVAL;
> - }
> /* Deal with TPS != HPS and huge pages */
> ret = postcopy_chunk_hostpages(ms, block);
> if (ret) {
> @@ -3097,12 +3052,9 @@ int ram_postcopy_send_discard_bitmap(MigrationState
> *ms)
> return ret;
> }
>
> - /*
> - * Update the unsentmap to be unsentmap = unsentmap | dirty
> - */
> - bitmap_or(unsentmap, unsentmap, bitmap, pages);
> #ifdef DEBUG_POSTCOPY
> - ram_debug_dump_bitmap(unsentmap, true, pages);
> + ram_debug_dump_bitmap(block->bmap, true,
> + block->used_length >> TARGET_PAGE_BITS);
> #endif
> }
> trace_ram_postcopy_send_discard_bitmap();
> @@ -3270,10 +3222,6 @@ static void ram_list_init_bitmaps(void)
> bitmap_set(block->bmap, 0, pages);
> block->clear_bmap_shift = shift;
> block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
> - if (migrate_postcopy_ram()) {
> - block->unsentmap = bitmap_new(pages);
> - bitmap_set(block->unsentmap, 0, pages);
> - }
> }
> }
> }
> --
> 2.17.1
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
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