From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50140) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a13LH-0002ku-3K for qemu-devel@nongnu.org; Mon, 23 Nov 2015 21:28:27 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a13LG-0004PG-6O for qemu-devel@nongnu.org; Mon, 23 Nov 2015 21:28:27 -0500 Date: Tue, 24 Nov 2015 10:28:14 +0800 From: Fam Zheng Message-ID: <20151124022814.GA26733@ad.usersys.redhat.com> References: <1448013593-14282-1-git-send-email-famz@redhat.com> <1448013593-14282-3-git-send-email-famz@redhat.com> <5653866A.2080003@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5653866A.2080003@redhat.com> Subject: Re: [Qemu-devel] [PATCH for 2.6 2/3] block: Hide HBitmap in block dirty bitmap interface List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow Cc: Kevin Wolf , vsementsov@virtuozzo.com, qemu-block@nongnu.org, Jeff Cody , qemu-devel@nongnu.org, mreitz@redhat.com, pbonzini@redhat.com On Mon, 11/23 16:34, John Snow wrote: > Hmm, what's the idea, here? > > This patch does a lot more than just hide hbitmap details from callers > of block_dirty_bitmap functions. > > So we're changing the backing hbitmap to always be one where g=0 and the > number of physical bits directly is (now) the same as the number of > 'virtual' bits, pre-patch. Then, to compensate, we handle the shift math > to convert the bitmap granularity to sector size and vice-versa in the > Block Dirty Bitmap layer instead of in the hbitmap layer. > > What's the benefit? It looks like we just pull all the implementation > details up from hbitmap and into BdrvDirtyBitmap, which I am not > immediately convinced of as being a benefit. It feels counter intuitive to me with hbitmap handling granularity, it makes it more like a HGranularityBitmap rather than HBitmap, and is unnecessarily complex to work on. Now it's simplified in that only one BdrvDirtyBitmap needs to care about the granularity, and which I think is a big benefit when we are going to extend the dirty bitmap interface, for example to serialize and deserialize for persistence. Fam