From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42788) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fb0IF-0001lD-JS for qemu-devel@nongnu.org; Thu, 05 Jul 2018 05:11:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fb0IC-0001nY-Dp for qemu-devel@nongnu.org; Thu, 05 Jul 2018 05:11:15 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:41614 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 1fb0IC-0001kX-89 for qemu-devel@nongnu.org; Thu, 05 Jul 2018 05:11:12 -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 37F3E407049A for ; Thu, 5 Jul 2018 09:11:11 +0000 (UTC) Date: Thu, 5 Jul 2018 17:11:06 +0800 From: Peter Xu Message-ID: <20180705091106.GB1389@xz-mi> References: <20180705031755.3254-1-peterx@redhat.com> <20180705031755.3254-2-peterx@redhat.com> <20180705090109.GB2538@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180705090109.GB2538@work-vm> 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: "Dr. David Alan Gilbert" Cc: qemu-devel@nongnu.org, Juan Quintela On Thu, Jul 05, 2018 at 10:01:09AM +0100, Dr. David Alan Gilbert wrote: > * 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) Sure thing. > > > /* > > * 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 Thanks! -- Peter Xu