From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40437) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fb08d-00071q-88 for qemu-devel@nongnu.org; Thu, 05 Jul 2018 05:01:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fb08Y-0005aB-1T for qemu-devel@nongnu.org; Thu, 05 Jul 2018 05:01:19 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:57724 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fb08X-0005W4-SM for qemu-devel@nongnu.org; Thu, 05 Jul 2018 05:01:13 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6C0A4401C876 for ; Thu, 5 Jul 2018 09:01:12 +0000 (UTC) Date: Thu, 5 Jul 2018 10:01:09 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20180705090109.GB2538@work-vm> References: <20180705031755.3254-1-peterx@redhat.com> <20180705031755.3254-2-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180705031755.3254-2-peterx@redhat.com> Subject: Re: [Qemu-devel] [PATCH for-3.0 1/9] migration: simplify check to use qemu file buffer List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: qemu-devel@nongnu.org, Juan Quintela * Peter Xu (peterx@redhat.com) wrote: > Firstly, renaming the old matching_page_sizes variable to > matching_target_page_size, which suites more to what it did (it only > checks against target page size rather than multiple page sizes). > Meanwhile, simplify the check logic a bit, and enhance the comments. > Should have no functional change. > > Signed-off-by: Peter Xu > --- > migration/ram.c | 17 +++++++++++------ > 1 file changed, 11 insertions(+), 6 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index 23cea47090..fbeb23f750 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -3580,7 +3580,7 @@ static int ram_load_postcopy(QEMUFile *f) > { > int flags = 0, ret = 0; > bool place_needed = false; > - bool matching_page_sizes = false; > + bool matching_target_page_size = false; > MigrationIncomingState *mis = migration_incoming_get_current(); > /* Temporary page that is later 'placed' */ > void *postcopy_host_page = postcopy_get_tmp_page(mis); > @@ -3620,7 +3620,7 @@ static int ram_load_postcopy(QEMUFile *f) > ret = -EINVAL; > break; > } > - matching_page_sizes = block->page_size == TARGET_PAGE_SIZE; > + matching_target_page_size = block->page_size == TARGET_PAGE_SIZE; That's OK, although 'matches_target_page_size' would be better wording. ('matching_target_page_size' implies we know something about the sources target page size) > /* > * Postcopy requires that we place whole host pages atomically; > * these may be huge pages for RAMBlocks that are backed by > @@ -3668,12 +3668,17 @@ static int ram_load_postcopy(QEMUFile *f) > > case RAM_SAVE_FLAG_PAGE: > all_zero = false; > - if (!place_needed || !matching_page_sizes) { > + if (!matching_target_page_size) { > + /* For huge pages, we always use temporary buffer */ > qemu_get_buffer(f, page_buffer, TARGET_PAGE_SIZE); > } else { > - /* Avoids the qemu_file copy during postcopy, which is > - * going to do a copy later; can only do it when we > - * do this read in one go (matching page sizes) > + /* > + * 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); But, yes I think that's right; since this is in ram_load_postcopy the only time we have !place_needed is in the not-last subpage of a hugepage (or host page > target_page), so that's already covered by the !matching_page_sizes check. Reviewed-by: Dr. David Alan Gilbert > -- > 2.17.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK