From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A368C3A5A2 for ; Fri, 23 Aug 2019 13:11:37 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5C63221848 for ; Fri, 23 Aug 2019 13:11:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5C63221848 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56004 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i19Ls-0008JG-Gt for qemu-devel@archiver.kernel.org; Fri, 23 Aug 2019 09:11:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36746) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i19Fc-0001Qu-3V for qemu-devel@nongnu.org; Fri, 23 Aug 2019 09:05:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i19Fa-0004ae-F6 for qemu-devel@nongnu.org; Fri, 23 Aug 2019 09:05:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39252) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i19Fa-0004aQ-73 for qemu-devel@nongnu.org; Fri, 23 Aug 2019 09:05:06 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 85F203090FC1; Fri, 23 Aug 2019 13:05:05 +0000 (UTC) Received: from work-vm (ovpn-117-244.ams2.redhat.com [10.36.117.244]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7B20A69506; Fri, 23 Aug 2019 13:05:04 +0000 (UTC) Date: Fri, 23 Aug 2019 14:05:02 +0100 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Message-ID: <20190823130502.GH2784@work-vm> References: <20190731144225.3784-1-richardw.yang@linux.intel.com> <20190731144225.3784-3-richardw.yang@linux.intel.com> <20190823110609.GF2784@work-vm> <20190823113801.GF9654@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20190823113801.GF9654@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Fri, 23 Aug 2019 13:05:05 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf waste for extra buf_index adjustment 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: quintela@redhat.com, Wei Yang , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrang=E9 (berrange@redhat.com) wrote: > On Fri, Aug 23, 2019 at 12:06:09PM +0100, Dr. David Alan Gilbert wrote: > > (Copying Dan in) > >=20 > > * Wei Yang (richardw.yang@linux.intel.com) wrote: > > > In add_to_iovec(), qemu_fflush() will be called if iovec is full. I= f > > > this happens, buf_index is reset. Currently, this is not checked an= d > > > buf_index would always been adjust with buf size. > > >=20 > > > This is not harmful, but will waste some space in file buffer. > >=20 > > That's a nice find. > >=20 > > > This patch make add_to_iovec() return 1 when it has flushed the fil= e. > > > Then the caller could check the return value to see whether it is > > > necessary to adjust the buf_index any more. > > >=20 > > > Signed-off-by: Wei Yang > >=20 > > Reviewed-by: Dr. David Alan Gilbert > >=20 > > (I wonder if there's a way to wrap that little add_to_iovec, check, a= dd > > to index, flush in a little wrapper). >=20 > Given the name "add_to_iovec" I think it is pretty surprising > that it calls "qemu_flush" at all. >=20 > It is also pretty wierd that we're checking two different > conditions in two different places. >=20 > Right now the code is essentially doing this: >=20 > if (f->iovcnt >=3D MAX_IOV_SIZE) { > qemu_fflush(f); > } > if (f->buf_index =3D=3D IO_BUF_SIZE) { > qemu_fflush(f); > } >=20 > Except that in the qemu_put_buffer_async() case, we're > only doing the first of these two checks. This feels > very odd indeed - I would have thought either it should > do both, or do neither. No, there's two separate types of buffers. There's f->buf which is a single allocated buffer in the QEMUFile with an offset buf_index, and there are arbitrary RAM pages added typically via qemu_put_buffer_async. The check for >=3D IO_BUF_SIZE is only done when adding to the f->buf, where as the check on f->iovcnt is done when you add an element to the iovec and that can happen potentially in either case. Dave > Assuming doing both flushs is ok for qemu_put_buffer_async > then I'd suggest renaming 'add_to_iovec' to 'queue_buffer' > and have that method do both of these qemu_fflush() calls. >=20 > > > --- > > > migration/qemu-file.c | 42 ++++++++++++++++++++++++++++-----------= --- > > > 1 file changed, 28 insertions(+), 14 deletions(-) > > >=20 > > > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > > > index 35c22605dd..05d9f42ddb 100644 > > > --- a/migration/qemu-file.c > > > +++ b/migration/qemu-file.c > > > @@ -343,8 +343,16 @@ int qemu_fclose(QEMUFile *f) > > > return ret; > > > } > > > =20 > > > -static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t s= ize, > > > - bool may_free) > > > +/* > > > + * Add buf to iovec. Do flush if iovec is full. > > > + * > > > + * Return values: > > > + * 1 iovec is full and flushed > > > + * 0 iovec is not flushed > > > + * > > > + */ > > > +static int add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t si= ze, > > > + bool may_free) > > > { > > > /* check for adjacent buffer and coalesce them */ > > > if (f->iovcnt > 0 && buf =3D=3D f->iov[f->iovcnt - 1].iov_base= + > > > @@ -362,7 +370,10 @@ static void add_to_iovec(QEMUFile *f, const ui= nt8_t *buf, size_t size, > > > =20 > > > if (f->iovcnt >=3D MAX_IOV_SIZE) { > > > qemu_fflush(f); > > > + return 1; > > > } > > > + > > > + return 0; > > > } > > > =20 > > > void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t= size, > > > @@ -391,10 +402,11 @@ void qemu_put_buffer(QEMUFile *f, const uint8= _t *buf, size_t size) > > > } > > > memcpy(f->buf + f->buf_index, buf, l); > > > f->bytes_xfer +=3D l; > > > - add_to_iovec(f, f->buf + f->buf_index, l, false); > > > - f->buf_index +=3D l; > > > - if (f->buf_index =3D=3D IO_BUF_SIZE) { > > > - qemu_fflush(f); > > > + if (!add_to_iovec(f, f->buf + f->buf_index, l, false)) { > > > + f->buf_index +=3D l; > > > + if (f->buf_index =3D=3D IO_BUF_SIZE) { > > > + qemu_fflush(f); > > > + } > > > } > > > if (qemu_file_get_error(f)) { > > > break; > > > @@ -412,10 +424,11 @@ void qemu_put_byte(QEMUFile *f, int v) > > > =20 > > > f->buf[f->buf_index] =3D v; > > > f->bytes_xfer++; > > > - add_to_iovec(f, f->buf + f->buf_index, 1, false); > > > - f->buf_index++; > > > - if (f->buf_index =3D=3D IO_BUF_SIZE) { > > > - qemu_fflush(f); > > > + if (!add_to_iovec(f, f->buf + f->buf_index, 1, false)) { > > > + f->buf_index++; > > > + if (f->buf_index =3D=3D IO_BUF_SIZE) { > > > + qemu_fflush(f); > > > + } > > > } > > > } > > > =20 > > > @@ -717,10 +730,11 @@ ssize_t qemu_put_compression_data(QEMUFile *f= , z_stream *stream, > > > } > > > =20 > > > qemu_put_be32(f, blen); > > > - add_to_iovec(f, f->buf + f->buf_index, blen, false); > > > - f->buf_index +=3D blen; > > > - if (f->buf_index =3D=3D IO_BUF_SIZE) { > > > - qemu_fflush(f); > > > + if (!add_to_iovec(f, f->buf + f->buf_index, blen, false)) { > > > + f->buf_index +=3D blen; > > > + if (f->buf_index =3D=3D IO_BUF_SIZE) { > > > + qemu_fflush(f); > > > + } > > > } > > > return blen + sizeof(int32_t); > > > } > > > --=20 > > > 2.17.1 > > >=20 > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > >=20 >=20 > Regards, > Daniel > --=20 > |: https://berrange.com -o- https://www.flickr.com/photos/dberr= ange :| > |: https://libvirt.org -o- https://fstop138.berrange= .com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberr= ange :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK