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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 36883C36000 for ; Fri, 21 Mar 2025 15:47:08 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tveZt-0005Vq-BG; Fri, 21 Mar 2025 11:46:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tveZR-0005St-Uw for qemu-devel@nongnu.org; Fri, 21 Mar 2025 11:46:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tveZM-0008M1-RM for qemu-devel@nongnu.org; Fri, 21 Mar 2025 11:46:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742571959; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=923fBdFpF7srfDlQezpPiv/YV/Ew1UvKsMi6Eia5/Ig=; b=E7SVklV5T7CZ/tFxa4fV6Bxwk3IPi6ZESJENirfHOvLMbPsH/j/faLdX6CQI7+CxuZHmwB DasInH6wh5Wv0BlSKdQwpewrwOWUthEdKsMrb5llevGFB6JqMtxNPOsCqZZVhUpYfJxxOU z4FsCO+VX45XKsbh4QboVjaXl0+OX3s= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-102-hxwevHI8PQWfWnThkMgiKg-1; Fri, 21 Mar 2025 11:45:55 -0400 X-MC-Unique: hxwevHI8PQWfWnThkMgiKg-1 X-Mimecast-MFC-AGG-ID: hxwevHI8PQWfWnThkMgiKg_1742571954 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E3C5A1933B41; Fri, 21 Mar 2025 15:45:53 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.52]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8016C19373C4; Fri, 21 Mar 2025 15:45:51 +0000 (UTC) Date: Fri, 21 Mar 2025 15:45:48 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Manish Mishra Cc: qemu-devel@nongnu.org, peterx@redhat.com, leobras@redhat.com, farosas@suse.de Subject: Re: [PATCH v3] QIOChannelSocket: Flush zerocopy socket error queue on sendmsg failure due to ENOBUF Message-ID: References: <20250317015231.241141-1-manish.mishra@nutanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250317015231.241141-1-manish.mishra@nutanix.com> User-Agent: Mutt/2.2.13 (2024-03-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.332, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Sun, Mar 16, 2025 at 09:52:31PM -0400, Manish Mishra wrote: > We allocate extra metadata SKBs in case of a zerocopy send. This metadata > memory is accounted for in the OPTMEM limit. If there is any error while > sending zerocopy packets or if zerocopy is skipped, these metadata SKBs are > queued in the socket error queue. This error queue is freed when userspace > reads it. > > Usually, if there are continuous failures, we merge the metadata into a single > SKB and free another one. As a result, it never exceeds the OPTMEM limit. > However, if there is any out-of-order processing or intermittent zerocopy > failures, this error chain can grow significantly, exhausting the OPTMEM limit. > As a result, all new sendmsg requests fail to allocate any new SKB, leading to > an ENOBUF error. Depending on the amount of data queued before the flush > (i.e., large live migration iterations), even large OPTMEM limits are prone to > failure. > > To work around this, if we encounter an ENOBUF error with a zerocopy sendmsg, > we flush the error queue and retry once more. > > V2: > 1. Removed the dirty_sync_missed_zero_copy migration stat. > 2. Made the call to qio_channel_socket_flush_internal() from > qio_channel_socket_writev() non-blocking. > > V3: > 1. Add the dirty_sync_missed_zero_copy migration stat again. These notes about changes each version should always be below the '---' line, because they shouldn't remain in the commit message when merged. > > Signed-off-by: Manish Mishra > --- > include/io/channel-socket.h | 5 +++ > io/channel-socket.c | 74 ++++++++++++++++++++++++++++++------- > 2 files changed, 65 insertions(+), 14 deletions(-) > > diff --git a/io/channel-socket.c b/io/channel-socket.c > index 608bcf066e..604ca9890d 100644 > --- a/io/channel-socket.c > +++ b/io/channel-socket.c > @@ -37,6 +37,12 @@ > > #define SOCKET_MAX_FDS 16 > > +#ifdef QEMU_MSG_ZEROCOPY > +static int qio_channel_socket_flush_internal(QIOChannel *ioc, > + bool block, > + Error **errp); > +#endif > + > SocketAddress * > qio_channel_socket_get_local_address(QIOChannelSocket *ioc, > Error **errp) > @@ -65,6 +71,7 @@ qio_channel_socket_new(void) > sioc->fd = -1; > sioc->zero_copy_queued = 0; > sioc->zero_copy_sent = 0; > + sioc->new_zero_copy_sent_success = FALSE; > > ioc = QIO_CHANNEL(sioc); > qio_channel_set_feature(ioc, QIO_CHANNEL_FEATURE_SHUTDOWN); > @@ -566,6 +573,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > size_t fdsize = sizeof(int) * nfds; > struct cmsghdr *cmsg; > int sflags = 0; > + bool zero_copy_flush_pending = TRUE; > > memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS)); > > @@ -612,9 +620,25 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > goto retry; > case ENOBUFS: > if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) { > - error_setg_errno(errp, errno, > - "Process can't lock enough memory for using MSG_ZEROCOPY"); > - return -1; > + /** > + * Socket error queueing may exhaust the OPTMEM limit. Try > + * flushing the error queue once. > + */ > + if (zero_copy_flush_pending) { > + ret = qio_channel_socket_flush_internal(ioc, false, errp); Hardcoding block==false isn't right. The socket may be in either blocking or non-blocking mode, and that needs to be taken into account, otherwise we'll get spurious failures in blocking mode if "flush" would otherwise want to block. > + if (ret < 0) { > + error_setg_errno(errp, errno, > + "Zerocopy flush failed"); > + return -1; > + } > + zero_copy_flush_pending = FALSE; > + goto retry; > + } else { > + error_setg_errno(errp, errno, > + "Process can't lock enough memory for " > + "using MSG_ZEROCOPY"); > + return -1; > + } > } > break; > } > @@ -725,8 +749,9 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > > > #ifdef QEMU_MSG_ZEROCOPY > -static int qio_channel_socket_flush(QIOChannel *ioc, > - Error **errp) > +static int qio_channel_socket_flush_internal(QIOChannel *ioc, > + bool block, > + Error **errp) > { > QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc); > struct msghdr msg = {}; > @@ -734,7 +759,6 @@ static int qio_channel_socket_flush(QIOChannel *ioc, > struct cmsghdr *cm; > char control[CMSG_SPACE(sizeof(*serr))]; > int received; > - int ret; > > if (sioc->zero_copy_queued == sioc->zero_copy_sent) { > return 0; > @@ -744,16 +768,19 @@ static int qio_channel_socket_flush(QIOChannel *ioc, > msg.msg_controllen = sizeof(control); > memset(control, 0, sizeof(control)); > > - ret = 1; > - > while (sioc->zero_copy_sent < sioc->zero_copy_queued) { > received = recvmsg(sioc->fd, &msg, MSG_ERRQUEUE); > if (received < 0) { > switch (errno) { > case EAGAIN: > - /* Nothing on errqueue, wait until something is available */ > - qio_channel_wait(ioc, G_IO_ERR); > - continue; > + if (block) { > + /* Nothing on errqueue, wait until something is > + * available. > + */ > + qio_channel_wait(ioc, G_IO_ERR); > + continue; > + } > + return 0; > case EINTR: > continue; > default: > @@ -791,13 +818,32 @@ static int qio_channel_socket_flush(QIOChannel *ioc, > /* No errors, count successfully finished sendmsg()*/ > sioc->zero_copy_sent += serr->ee_data - serr->ee_info + 1; > > - /* If any sendmsg() succeeded using zero copy, return 0 at the end */ > + /* If any sendmsg() succeeded using zero copy, mark zerocopy success */ > if (serr->ee_code != SO_EE_CODE_ZEROCOPY_COPIED) { > - ret = 0; > + sioc->new_zero_copy_sent_success = TRUE; > } > } > > - return ret; > + return 0; > +} > + > +static int qio_channel_socket_flush(QIOChannel *ioc, > + Error **errp) > +{ > + QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc); > + int ret; > + > + ret = qio_channel_socket_flush_internal(ioc, true, errp); > + if (ret < 0) { > + return ret; > + } > + > + if (sioc->new_zero_copy_sent_success) { > + sioc->new_zero_copy_sent_success = FALSE; > + return 0; > + } > + > + return 1; > } > > #endif /* QEMU_MSG_ZEROCOPY */ > -- > 2.43.0 > With 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 :|