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=-7.8 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 84666C3A59E for ; Sat, 24 Aug 2019 16:24:01 +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 4E8EE2133F for ; Sat, 24 Aug 2019 16:24:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bPUreMh3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E8EE2133F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38566 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i1Ypc-0002HF-F4 for qemu-devel@archiver.kernel.org; Sat, 24 Aug 2019 12:24:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35783) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i1Yo1-00019g-7c for qemu-devel@nongnu.org; Sat, 24 Aug 2019 12:22:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i1Ynz-0001YN-P4 for qemu-devel@nongnu.org; Sat, 24 Aug 2019 12:22:21 -0400 Received: from mail-ed1-x543.google.com ([2a00:1450:4864:20::543]:38761) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1i1Ynz-0001X4-Ho for qemu-devel@nongnu.org; Sat, 24 Aug 2019 12:22:19 -0400 Received: by mail-ed1-x543.google.com with SMTP id r12so18921056edo.5 for ; Sat, 24 Aug 2019 09:22:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:reply-to:references:mime-version :content-disposition:in-reply-to:user-agent; bh=xV35PQTVCpcmCYGCnp4650KahGAkmXbrekQ72U/q1FE=; b=bPUreMh3HoM3q5c0q8lX+G/qA5no5PkBgmnjWI6f30CHUZdwRQ30KaydkKDto9c6xg rHuWMKaUrDnfPARPPYbrmSrkNEM0TD/N+htH+1oyaelBFoT/w8WSG1Vpsm+pQpaWLVRY U0yinWnzCiIrCZP0siMpfDjmnYEhbCbB5ScpEzt2hX9sjj1XEHao0Fv/8w71kksArrUa E8Svkx7vOyKFqYl+nEiX7M0YplBIuj6neOgyOtvabBDuj8OtVd0rWTI4lu6BHhiAQIO8 AA9DCLj4sGt25wxiG7UTfbOoxu3BMReLkhn6sUoob/Hd98rzzspHDJvuljZ+tHETLpsp orTA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:reply-to :references:mime-version:content-disposition:in-reply-to:user-agent; bh=xV35PQTVCpcmCYGCnp4650KahGAkmXbrekQ72U/q1FE=; b=nwGEXqSJCcXnSxUrvbO7F8JfkeSTb2srR2zUsquHSEXGmrlkPAQPl+8OuPEgV40pbh OexfATEU0PDCuLoimHvkiL/nd2z3pUoZGy3/T27Wiw1KcHCw5PkKcYJlen/pd8bjgpBz uaE2g78hhQwt3i2cSzBQ2J3/8y1GP9t8j5HLzpAUb8Nib23mHzqDjD5mks2xTlQVHXUx rEqaCtjffkkd27ETStZrLzSoKz+ERmv9f+eC4QluAmZ34K1R6ylOttcfZ7VMaUe3IuMf kFgNhxP9KzGNpbiB6xTAaH5JBUTdUrCBVURbB7BU83AMrZSzV+LWc/lw0779H40ZvrLL 9QSw== X-Gm-Message-State: APjAAAX6pQzngBS16xah0t84xM6AOtPRITRrZXw7eNHAAibhWaCJHlmP ZANbUI86QadilX8Cr+Qaj10= X-Google-Smtp-Source: APXvYqzPcMSmR3Ysl7hpWnOoO5sxgHEq4WI+KEcETYpQDt8o631vl3kDBy27dl9MSijS0uK7mtc6Sg== X-Received: by 2002:a05:6402:1214:: with SMTP id c20mr10235588edw.111.1566663738414; Sat, 24 Aug 2019 09:22:18 -0700 (PDT) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id y14sm1274421ejo.76.2019.08.24.09.22.17 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 24 Aug 2019 09:22:17 -0700 (PDT) Date: Sat, 24 Aug 2019 16:22:16 +0000 From: Wei Yang To: "Dr. David Alan Gilbert" Message-ID: <20190824162216.ypo6vp2c6u2om4o7@master> 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> <20190823130502.GH2784@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190823130502.GH2784@work-vm> User-Agent: NeoMutt/20170113 (1.7.2) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2a00:1450:4864:20::543 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: , Reply-To: Wei Yang Cc: qemu-devel@nongnu.org, "Daniel P. Berrang?" , Wei Yang , quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Aug 23, 2019 at 02:05:02PM +0100, Dr. David Alan Gilbert wrote: >* Daniel P. Berrang? (berrange@redhat.com) wrote: >> On Fri, Aug 23, 2019 at 12:06:09PM +0100, Dr. David Alan Gilbert wrote: >> > (Copying Dan in) >> > >> > * Wei Yang (richardw.yang@linux.intel.com) wrote: >> > > In add_to_iovec(), qemu_fflush() will be called if iovec is full. If >> > > this happens, buf_index is reset. Currently, this is not checked and >> > > buf_index would always been adjust with buf size. >> > > >> > > This is not harmful, but will waste some space in file buffer. >> > >> > That's a nice find. >> > >> > > This patch make add_to_iovec() return 1 when it has flushed the file. >> > > Then the caller could check the return value to see whether it is >> > > necessary to adjust the buf_index any more. >> > > >> > > Signed-off-by: Wei Yang >> > >> > Reviewed-by: Dr. David Alan Gilbert >> > >> > (I wonder if there's a way to wrap that little add_to_iovec, check, add >> > to index, flush in a little wrapper). >> >> Given the name "add_to_iovec" I think it is pretty surprising >> that it calls "qemu_flush" at all. >> >> It is also pretty wierd that we're checking two different >> conditions in two different places. >> >> Right now the code is essentially doing this: >> >> if (f->iovcnt >= MAX_IOV_SIZE) { >> qemu_fflush(f); >> } >> if (f->buf_index == IO_BUF_SIZE) { >> qemu_fflush(f); >> } >> >> 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. > qemu_put_buffer_async is the only one which put a range not in f->buf into the iovec. And one thing confused me is even its name is async, add_to_iovec still would call qemu_fflush when iovec is full. So it is not a always async function. >From the function name, it is a little difficult to differentiate qemu_put_buffer and qemu_put_buffer_async. >The check for >= 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. >> >> > > --- >> > > migration/qemu-file.c | 42 ++++++++++++++++++++++++++++-------------- >> > > 1 file changed, 28 insertions(+), 14 deletions(-) >> > > >> > > 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; >> > > } >> > > >> > > -static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size, >> > > - 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 size, >> > > + bool may_free) >> > > { >> > > /* check for adjacent buffer and coalesce them */ >> > > if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base + >> > > @@ -362,7 +370,10 @@ static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size, >> > > >> > > if (f->iovcnt >= MAX_IOV_SIZE) { >> > > qemu_fflush(f); >> > > + return 1; >> > > } >> > > + >> > > + return 0; >> > > } >> > > >> > > 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 += l; >> > > - add_to_iovec(f, f->buf + f->buf_index, l, false); >> > > - f->buf_index += l; >> > > - if (f->buf_index == IO_BUF_SIZE) { >> > > - qemu_fflush(f); >> > > + if (!add_to_iovec(f, f->buf + f->buf_index, l, false)) { >> > > + f->buf_index += l; >> > > + if (f->buf_index == 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) >> > > >> > > f->buf[f->buf_index] = v; >> > > f->bytes_xfer++; >> > > - add_to_iovec(f, f->buf + f->buf_index, 1, false); >> > > - f->buf_index++; >> > > - if (f->buf_index == 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 == IO_BUF_SIZE) { >> > > + qemu_fflush(f); >> > > + } >> > > } >> > > } >> > > >> > > @@ -717,10 +730,11 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream, >> > > } >> > > >> > > qemu_put_be32(f, blen); >> > > - add_to_iovec(f, f->buf + f->buf_index, blen, false); >> > > - f->buf_index += blen; >> > > - if (f->buf_index == IO_BUF_SIZE) { >> > > - qemu_fflush(f); >> > > + if (!add_to_iovec(f, f->buf + f->buf_index, blen, false)) { >> > > + f->buf_index += blen; >> > > + if (f->buf_index == IO_BUF_SIZE) { >> > > + qemu_fflush(f); >> > > + } >> > > } >> > > return blen + sizeof(int32_t); >> > > } >> > > -- >> > > 2.17.1 >> > > >> > -- >> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK >> > >> >> Regards, >> Daniel >> -- >> |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| >> |: https://libvirt.org -o- https://fstop138.berrange.com :| >> |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >-- >Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK -- Wei Yang Help you, Help me