From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59344) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cbQNk-0003h3-MN for qemu-devel@nongnu.org; Wed, 08 Feb 2017 06:25:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cbQNh-00041R-IS for qemu-devel@nongnu.org; Wed, 08 Feb 2017 06:25:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53276) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cbQNh-00041J-4B for qemu-devel@nongnu.org; Wed, 08 Feb 2017 06:25:49 -0500 Date: Wed, 8 Feb 2017 11:25:43 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20170208112542.GC2341@work-vm> References: <1486118198-8965-1-git-send-email-ashijeetacharya@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1486118198-8965-1-git-send-email-ashijeetacharya@gmail.com> Subject: Re: [Qemu-devel] [PATCH v2] migrate: Introduce zero RAM checks to skip RAM migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ashijeet Acharya Cc: thuth@redhat.com, quintela@redhat.com, amit.shah@redhat.com, berrange@redhat.com, pbonzini@redhat.com, groug@kaod.org, qemu-devel@nongnu.org * Ashijeet Acharya (ashijeetacharya@gmail.com) wrote: > Migration of a "none" machine with no RAM crashes abruptly as > bitmap_new() fails and thus aborts. Instead place zero RAM checks at > appropriate places to skip migration of RAM in this case and complete > migration successfully for devices only. > > Signed-off-by: Ashijeet Acharya Yes it seems to work, but there is a small bug, if we look at: static void ram_migration_cleanup(void *opaque) { /* caller have hold iothread lock or is in a bh, so there is * no writing race against this migration_bitmap */ struct BitmapRcu *bitmap = migration_bitmap_rcu; atomic_rcu_set(&migration_bitmap_rcu, NULL); if (bitmap) { memory_global_dirty_log_stop(); call_rcu(bitmap, migration_bitmap_free, rcu); } we see it doesn't cause memory_global_dirty_log_stop if migration_bitmap_rcu is NULL; so we end up still calling dirty_log_start in ram_save_init but never call stop. I suggest you change it to: migration_bitmap_rcu = g_new0(struct BitmapRcu, 1); if (ram_bytes_total()) { ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS; migration_bitmap_rcu->bmap = bitmap_new(ram_bitmap_pages); bitmap_set(migration_bitmap_rcu->bmap, 0, ram_bitmap_pages); The cleanup routine still causes the dirty_log_stop() then. Dave > --- > Changes in v2: > - try to migrate successfully by skipping RAM (Paolo, Greg) > - drop the idea of erroring out and failing nicely > migration/ram.c | 22 +++++++++++++++------- > 1 file changed, 15 insertions(+), 7 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index ef8fadf..2f19566 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -1325,6 +1325,11 @@ static int ram_find_and_save_block(QEMUFile *f, bool last_stage, > ram_addr_t dirty_ram_abs; /* Address of the start of the dirty page in > ram_addr_t space */ > > + /* No dirty page as there is zero RAM */ > + if (!ram_bytes_total()) { > + return pages; > + } > + > pss.block = last_seen_block; > pss.offset = last_offset; > pss.complete_round = false; > @@ -1912,14 +1917,17 @@ static int ram_save_init_globals(void) > bytes_transferred = 0; > reset_ram_globals(); > > - ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS; > - migration_bitmap_rcu = g_new0(struct BitmapRcu, 1); > - migration_bitmap_rcu->bmap = bitmap_new(ram_bitmap_pages); > - bitmap_set(migration_bitmap_rcu->bmap, 0, ram_bitmap_pages); > + /* Skip setting bitmap if there is no RAM */ > + if (ram_bytes_total()) { > + ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS; > + migration_bitmap_rcu = g_new0(struct BitmapRcu, 1); > + migration_bitmap_rcu->bmap = bitmap_new(ram_bitmap_pages); > + bitmap_set(migration_bitmap_rcu->bmap, 0, ram_bitmap_pages); > > - if (migrate_postcopy_ram()) { > - migration_bitmap_rcu->unsentmap = bitmap_new(ram_bitmap_pages); > - bitmap_set(migration_bitmap_rcu->unsentmap, 0, ram_bitmap_pages); > + if (migrate_postcopy_ram()) { > + migration_bitmap_rcu->unsentmap = bitmap_new(ram_bitmap_pages); > + bitmap_set(migration_bitmap_rcu->unsentmap, 0, ram_bitmap_pages); > + } > } > > /* > -- > 2.6.2 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK