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migration: do not sent zero pages in bulk stage

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during bulk stage of ram migration if a page is a
zero page do not send it at all.
the memory at the destination reads as zero anyway.

even if there is an madvise with QEMU_MADV_DONTNEED
at the target upon receipt of a zero page I have observed
that the target starts swapping if the memory is overcommitted.
it seems that the pages are dropped asynchronously.

this patch also updates QMP to return the number of
skipped pages in MigrationStats.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Peter Lieven 2013-03-26 10:58:37 +01:00 • committed by Juan Quintela
parent 78d07ae7ac
commit f1c72795af
6 changed files with 32 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

24
arch_init.c
View file

@ -183,6 +183,7 @@ int64_t xbzrle_cache_resize(int64_t new_size)
/* accounting for migration statistics */
typedef struct AccountingInfo {
uint64_t dup_pages;
uint64_t skipped_pages;
uint64_t norm_pages;
uint64_t iterations;
uint64_t xbzrle_bytes;
@ -208,6 +209,16 @@ uint64_t dup_mig_pages_transferred(void)
return acct_info.dup_pages;
}
uint64_t skipped_mig_bytes_transferred(void)
{
return acct_info.skipped_pages * TARGET_PAGE_SIZE;
}
uint64_t skipped_mig_pages_transferred(void)
{
return acct_info.skipped_pages;
}
uint64_t norm_mig_bytes_transferred(void)
{
return acct_info.norm_pages * TARGET_PAGE_SIZE;
@ -440,10 +451,15 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
bytes_sent = -1;
if (is_zero_page(p)) {
acct_info.dup_pages++;
bytes_sent = save_block_hdr(f, block, offset, cont,
RAM_SAVE_FLAG_COMPRESS);
qemu_put_byte(f, 0);
bytes_sent++;
if (!ram_bulk_stage) {
bytes_sent = save_block_hdr(f, block, offset, cont,
RAM_SAVE_FLAG_COMPRESS);
qemu_put_byte(f, 0);
bytes_sent++;
} else {
acct_info.skipped_pages++;
bytes_sent = 0;
}
} else if (migrate_use_xbzrle()) {
current_addr = block->offset + offset;
bytes_sent = save_xbzrle_page(f, p, current_addr, block,