From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56345) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WR0dm-0003dk-FM for qemu-devel@nongnu.org; Fri, 21 Mar 2014 10:41:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WR0df-0007Vi-Ca for qemu-devel@nongnu.org; Fri, 21 Mar 2014 10:41:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14947) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WR0df-0007VV-2v for qemu-devel@nongnu.org; Fri, 21 Mar 2014 10:41:39 -0400 Date: Fri, 21 Mar 2014 14:41:32 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20140321144131.GB8476@work-vm> References: <1395399490-13295-1-git-send-email-dgilbert@redhat.com> <85431B4A-46CD-462D-9464-E9D9ACCA25FD@icloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <85431B4A-46CD-462D-9464-E9D9ACCA25FD@icloud.com> Subject: Re: [Qemu-devel] [PATCH 1/1] Count used RAMBlock pages for migration_dirty_pages List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ???? Cc: qemu-devel@nongnu.org, quintela@redhat.com * ???? (chenliang0016@icloud.com) wrote: > > > From: "Dr. David Alan Gilbert" > > > > This is a fix for a bug* triggered by a migration after hot unplugging > > a few virtio-net NICs, that caused migration never to converge, because > > 'migration_dirty_pages' is incorrectly initialised. > > > > 'migration_dirty_pages' is used as a tally of the number of outstanding > > dirty pages, to give the migration code an idea of how much more data > > will need to be transferred, and thus whether it can end the iterative > > phase. > > > > It was initialised to the total size of the RAMBlock address space, > > however hotunplug can leave this space sparse, and hence > > migration_dirty_pages ended up too large. > > > > Note that the code tries to be careful when counting to deal with > > RAMBlocks that share the same end/start page - I don't know > > if this is actually possible and it does complicate the code, > > but since there was other code that dealt with unaligned RAMBlocks > > it seemed possible. > > > > Signed-off-by: Dr. David Alan Gilbert > > > > (* https://bugzilla.redhat.com/show_bug.cgi?id=1074913 ) > > --- > > arch_init.c | 41 +++++++++++++++++++++++++++++++++++++---- > > 1 file changed, 37 insertions(+), 4 deletions(-) > > > > diff --git a/arch_init.c b/arch_init.c > > index f18f42e..ef0e98d 100644 > > --- a/arch_init.c > > +++ b/arch_init.c > > @@ -727,11 +727,8 @@ static void reset_ram_globals(void) > > static int ram_save_setup(QEMUFile *f, void *opaque) > > { > > RAMBlock *block; > > - int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS; > > + int64_t ram_bitmap_pages; > > > > - migration_bitmap = bitmap_new(ram_pages); > > - bitmap_set(migration_bitmap, 0, ram_pages); > > - migration_dirty_pages = ram_pages; > > mig_throttle_on = false; > > dirty_rate_high_cnt = 0; > > > > @@ -770,6 +767,42 @@ static int ram_save_setup(QEMUFile *f, void *opaque) > > bytes_transferred = 0; > > reset_ram_globals(); > > > > + ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS; > > + migration_bitmap = bitmap_new(ram_bitmap_pages); > > + bitmap_set(migration_bitmap, 0, ram_bitmap_pages); > > + /* > > + * Count the total number of pages used by ram blocks. We clear the dirty > > + * bit for the start/end of each ramblock as we go so that we don't double > > + * count ramblocks that have overlapping pages - at entry the whole dirty > > + * bitmap is set. > > + */ > > + migration_dirty_pages = 0; > > + QTAILQ_FOREACH(block, &ram_list.blocks, next) { > > + uint64_t block_pages = 0; > > + ram_addr_t saddr, eaddr; > > + > > + saddr = block->mr->ram_addr; > > + eaddr = saddr + block->length - 1; > > + saddr /= TARGET_PAGE_SIZE; > > + eaddr /= TARGET_PAGE_SIZE; > > + > > + /* Do the end pages of the range, that might be shared with others */ > > + block_pages += test_and_clear_bit(saddr, migration_bitmap); > > + block_pages += test_and_clear_bit(eaddr, migration_bitmap); > > + > > + if ((saddr + 1) < eaddr) { > > + block_pages += eaddr - (saddr + 1); > > + } > > + migration_dirty_pages += block_pages; > > + /*fprintf(stderr, "ram_save_setup: %s s/e=%zx/%zx page s/e=%zx/%zx" > > + " bp=%zu\n", > > + block->idstr, block->mr->ram_addr, > > + block->mr->ram_addr+block->length-1, > > + saddr, eaddr, block_pages); */ > > + } > > + /* and set the bits again that got used for our overlap check */ > > + bitmap_set(migration_bitmap, 0, ram_bitmap_pages); > > maybe it should like this: > bitmap_set(migration_bitmap, 0, last_ram_offset() >> TARGET_PAGE_BITS); > Because there are some space sparse. No, ram_bitmap_pages is already equal to last_ram_offset() >> TARGET_PAGE_BITS The loop has been calculating migration_dirty_pages and hasn't touched ram_bitmap_pages. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK