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Fri, 4 Oct 2019 16:31:56 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-204-31.brq.redhat.com [10.40.204.31]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BB6BB6012C; Fri, 4 Oct 2019 16:31:52 +0000 (UTC) Subject: Re: [PATCH 3/4] block/mirror: support unaligned write in active mirror To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20190912151338.21225-1-vsementsov@virtuozzo.com> <20190912151338.21225-4-vsementsov@virtuozzo.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <6fd6a449-0443-ecfa-0eec-23e3b515b303@redhat.com> Date: Fri, 4 Oct 2019 18:31:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <20190912151338.21225-4-vsementsov@virtuozzo.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="NnRTkHir4cCIKYDsS0FEEjxOGi1iPk5C0" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.69]); Fri, 04 Oct 2019 16:31:56 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, den@openvz.org, jsnow@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --NnRTkHir4cCIKYDsS0FEEjxOGi1iPk5C0 Content-Type: multipart/mixed; boundary="y6cCdsqYswb8L3Wjn3vovrA32MRNgMHpp" --y6cCdsqYswb8L3Wjn3vovrA32MRNgMHpp Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 12.09.19 17:13, Vladimir Sementsov-Ogievskiy wrote: > Prior 9adc1cb49af8d do_sync_target_write had a bug: it reset aligned-up= > region in the dirty bitmap, which means that we may not copy some bytes= > and assume them copied, which actually leads to producing corrupted > target. >=20 > So 9adc1cb49af8d forced dirty bitmap granularity to be > request_alignment for mirror-top filter, so we are not working with > unaligned requests. However forcing large alignment obviously decreases= > performance of unaligned requests. >=20 > This commit provides another solution for the problem: if unaligned > padding is already dirty, we can safely ignore it, as > 1. It's dirty, it will be copied by mirror_iteration anyway > 2. It's dirty, so skipping it now we don't increase dirtiness of the > bitmap and therefore don't damage "synchronicity" of the > write-blocking mirror. >=20 > If unaligned padding is not dirty, we just write it, no reason to touch= > dirty bitmap if we succeed (on failure we'll set the whole region > ofcourse, but we loss "synchronicity" on failure anyway). >=20 > Note: we need to disable dirty_bitmap, otherwise we will not be able to= > see in do_sync_target_write bitmap state before current operation. We > may of course check dirty bitmap before the operation in > bdrv_mirror_top_do_write and remember it, but we don't need active > dirty bitmap for write-blocking mirror anyway. >=20 > New code-path is unused until the following commit reverts > 9adc1cb49af8d. >=20 > Suggested-by: Denis V. Lunev > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > block/mirror.c | 39 ++++++++++++++++++++++++++++++++++++++- > 1 file changed, 38 insertions(+), 1 deletion(-) >=20 > diff --git a/block/mirror.c b/block/mirror.c > index d176bf5920..d192f6a96b 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -1204,6 +1204,39 @@ do_sync_target_write(MirrorBlockJob *job, Mirror= Method method, > QEMUIOVector *qiov, int flags) > { > int ret; > + size_t qiov_offset =3D 0; > + > + if (!QEMU_IS_ALIGNED(offset, job->granularity) && > + bdrv_dirty_bitmap_get(job->dirty_bitmap, offset)) { > + /* > + * Dirty unaligned padding > + * 1. It's already dirty, no damage to "actively_synced" i= f we just > + * skip unaligned part. > + * 2. If we copy it, we can't reset corresponding bit in > + * dirty_bitmap as there may be some "dirty" bytes stil= l not > + * copied. > + * So, just ignore it. > + */ > + qiov_offset =3D QEMU_ALIGN_UP(offset, job->granularity) - = offset; > + if (bytes <=3D qiov_offset) { > + /* nothing to do after shrink */ > + return; > + } > + offset +=3D qiov_offset; > + bytes -=3D qiov_offset; > + } > + > + if (!QEMU_IS_ALIGNED(offset + bytes, job->granularity) && > + bdrv_dirty_bitmap_get(job->dirty_bitmap, offset + bytes - 1)) > + { > + uint64_t tail =3D (offset + bytes) % job->granularity; > + > + if (bytes <=3D tail) { > + /* nothing to do after shrink */ > + return; > + } > + bytes -=3D tail; > + } > =20 > bdrv_reset_dirty_bitmap(job->dirty_bitmap, offset, bytes); > =20 The bdrv_set_dirty_bitmap() in the error case below needs to use the original offset/bytes, I suppose. Apart from that, looks good to me. Max --y6cCdsqYswb8L3Wjn3vovrA32MRNgMHpp-- --NnRTkHir4cCIKYDsS0FEEjxOGi1iPk5C0 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl2Xc/cACgkQ9AfbAGHV z0BHKQf/YTvtx4f7SKBt+T9Nhb9ORb76cjz4TGrajZd/Ox+XsHnRSK5nyotK+nc+ VljtG2Q/qnr7mBFTCu6E+fbKclsWCkHXDRDXP/RVau8814L35cfPf2qROwYx2mnM m5loesf58K+PKoyulkzDWpmEsc7kduNkdO3ZfWCmb/z+IO5X4p7S3AM/QzggJsE+ JOmkCDkgCdfErBscropthejhvUcRM+cEsmuUtRbUxznv1fhbB6kZn+YwctmT6E1q dPakREbHbdgtEyS8cMbpYr52Auwv90Ks5V/Mg/Yd8c1MVuU3/Cb++sw9LUnRUJni Xqh780TKSpojbCzUWOUugsZRdhPtUg== =5MmK -----END PGP SIGNATURE----- --NnRTkHir4cCIKYDsS0FEEjxOGi1iPk5C0--