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 1A729CCF9FF for ; Fri, 31 Oct 2025 14:00:25 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vEpfa-0000Va-ON; Fri, 31 Oct 2025 09:59:58 -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 1vEpfY-0000VN-RM for qemu-devel@nongnu.org; Fri, 31 Oct 2025 09:59:56 -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 1vEpfQ-0003Hy-IB for qemu-devel@nongnu.org; Fri, 31 Oct 2025 09:59:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761919185; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=stuMcp2HDAWTrsB12IWigVUpixcN3VROJ5irrSVVg4I=; b=RbP7f1654jE7oLGlUXW25wppE5la0mouWK3UsjeeiQmYK02Q+wNTdXTm1KfSbKJK8Wx9xi kS9TaujcqSn8wpSF80ad8d85CJvLEI2mP/Pe/uGm/Hq3Ua7ka41kJTKBfO+noj04uwAS7I fYtf7FkvbxomlFgr7Y9vGjCYIriBJHY= Received: from mx-prod-mc-03.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-86-SVbJLH4wMembZenRPNAtJA-1; Fri, 31 Oct 2025 09:59:40 -0400 X-MC-Unique: SVbJLH4wMembZenRPNAtJA-1 X-Mimecast-MFC-AGG-ID: SVbJLH4wMembZenRPNAtJA_1761919179 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 458231955DA6; Fri, 31 Oct 2025 13:59:37 +0000 (UTC) Received: from redhat.com (dhcp-17-192.lcy.redhat.com [10.42.17.192]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7F52419540DA; Fri, 31 Oct 2025 13:59:35 +0000 (UTC) Date: Fri, 31 Oct 2025 13:59:32 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Tejus GK Cc: qemu-devel@nongnu.org, Manish Mishra , Peter Xu , Fabiano Rosas Subject: Re: [PATCH v7 2/2] QIOChannelSocket: flush zerocopy socket error queue on sendmsg failure due to ENOBUF Message-ID: References: <20251024131546.929499-1-tejus.gk@nutanix.com> <20251024131546.929499-3-tejus.gk@nutanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20251024131546.929499-3-tejus.gk@nutanix.com> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, T_SPF_TEMPERROR=0.01 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 Fri, Oct 24, 2025 at 01:15:43PM +0000, Tejus GK wrote: > From: Manish Mishra > > The kernel allocates extra metadata SKBs in case of a zerocopy send, > eventually used for zerocopy's notification mechanism. This metadata > memory is accounted for in the OPTMEM limit. The kernel queues > completion notifications on the socket error queue and this error queue > is freed when userspace reads it. > > Usually, in the case of in-order processing, the kernel will batch the > notifications and merge the metadata into a single SKB and free the > rest. 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, flush the error queue and retry once more. > > Co-authored-by: Manish Mishra > Signed-off-by: Tejus GK > --- > include/io/channel-socket.h | 5 +++ > io/channel-socket.c | 80 ++++++++++++++++++++++++++++++------- > 2 files changed, 71 insertions(+), 14 deletions(-) Signed-off-by: Daniel P. Berrangé > SocketAddress * > qio_channel_socket_get_local_address(QIOChannelSocket *ioc, > Error **errp) > @@ -66,6 +72,7 @@ qio_channel_socket_new(void) > sioc->zero_copy_queued = 0; > sioc->zero_copy_sent = 0; > sioc->blocking = false; > + sioc->new_zero_copy_sent_success = FALSE; Needs to be 'false' > > ioc = QIO_CHANNEL(sioc); > qio_channel_set_feature(ioc, QIO_CHANNEL_FEATURE_SHUTDOWN); > @@ -618,6 +625,8 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > size_t fdsize = sizeof(int) * nfds; > struct cmsghdr *cmsg; > int sflags = 0; > + bool blocking = sioc->blocking; > + bool zerocopy_flushed_once = false; > > memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS)); > > @@ -664,9 +673,24 @@ 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 (!zerocopy_flushed_once) { > + ret = qio_channel_socket_flush_internal(ioc, blocking, > + errp); > + if (ret < 0) { > + return -1; > + } > + zerocopy_flushed_once = TRUE; ... 'true'.. > @@ -843,13 +876,32 @@ 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; ...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; ...false.... Since these are trivial changes, i'll make them when applying this patch, so no need to re-send. 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 :|