On Tue, Jan 24, 2023 at 01:20:37PM +0000, Dr. David Alan Gilbert wrote:
> > @@ -3970,7 +3984,8 @@ int ram_load_postcopy(QEMUFile *f, int channel)
> > break;
> > }
> > tmp_page->target_pages++;
> > - matches_target_page_size = block->page_size ==
> > TARGET_PAGE_SIZE;
> > + matches_target_page_size =
> > + migration_ram_pagesize(block) == TARGET_PAGE_SIZE;
> > /*
> > * Postcopy requires that we place whole host pages atomically;
> > * these may be huge pages for RAMBlocks that are backed by
>
> Hmm do you really want this change?
Yes that's intended. I want to reuse the same logic here when receiving
small pages from huge pages, just like when we're receiving small pages on
non-hugetlb mappings.
matches_target_page_size majorly affects two things:
1) For a small zero page, whether we want to pre-set the page_buffer, or
simply use postcopy_place_page_zero():
case RAM_SAVE_FLAG_ZERO:
ch = qemu_get_byte(f);
/*
* Can skip to set page_buffer when
* this is a zero page and (block->page_size == TARGET_PAGE_SIZE).
*/
if (ch || !matches_target_page_size) {
memset(page_buffer, ch, TARGET_PAGE_SIZE);
}
2) For normal page, whether we need to use a page buffer or we can
directly reuse the page buffer in QEMUFile:
if (!matches_target_page_size) {
/* For huge pages, we always use temporary buffer */
qemu_get_buffer(f, page_buffer, TARGET_PAGE_SIZE);
} else {
/*
* For small pages that matches target page size, we
* avoid the qemu_file copy. Instead we directly use
* the buffer of QEMUFile to place the page. Note: we
* cannot do any QEMUFile operation before using that
* buffer to make sure the buffer is valid when
* placing the page.
*/
qemu_get_buffer_in_place(f, (uint8_t **)&place_source,
TARGET_PAGE_SIZE);
}
Here:
I want 1) to reuse postcopy_place_page_zero(). For the doublemap case,
it'll reuse postcopy_tmp_zero_page() (because qemu_ram_is_uf_zeroable()
will return false for such a ramblock).
I want 2) to reuse qemu_get_buffer_in_place(), so we avoid a copy process
for the small page which is faster (even if it's hugetlb backed, now we can
reuse the qemufile buffer safely).
Thanks,
--
Peter Xu
