On 15/01/2016 10:48, Liang Li wrote: > Now that VM's RAM pages are initialized to zero, (VM's RAM is allcated > with the mmap() and MAP_ANONYMOUS option, or mmap() without MAP_SHARED > if hugetlbfs is used.) so there is no need to send the zero page header > to destination. > > For guest just uses a small portions of RAM, this change can avoid > allocating all the guest's RAM pages in the destination node after > live migration. Another benefit is destination QEMU can save lots of > CPU cycles for zero page checking. > > Signed-off-by: Liang Li <liang.z...@intel.com>
This does not work. Depending on the board, some pages are written by QEMU before the guest starts. If the guest rewrites them with zeroes, this change breaks migration. Paolo > --- > migration/ram.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index 4e606ab..c4821d1 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -705,10 +705,12 @@ static int save_zero_page(QEMUFile *f, RAMBlock *block, > ram_addr_t offset, > > if (is_zero_range(p, TARGET_PAGE_SIZE)) { > acct_info.dup_pages++; > - *bytes_transferred += save_page_header(f, block, > - offset | > RAM_SAVE_FLAG_COMPRESS); > - qemu_put_byte(f, 0); > - *bytes_transferred += 1; > + if (!ram_bulk_stage) { > + *bytes_transferred += save_page_header(f, block, offset | > + RAM_SAVE_FLAG_COMPRESS); > + qemu_put_byte(f, 0); > + *bytes_transferred += 1; > + } > pages = 1; > } > >