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 C9315C369AB for ; Tue, 15 Apr 2025 09:28:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u4cag-00037y-Qg; Tue, 15 Apr 2025 05:28:28 -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 1u4caV-000341-5H for qemu-devel@nongnu.org; Tue, 15 Apr 2025 05:28:18 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u4caQ-0002XP-Tu for qemu-devel@nongnu.org; Tue, 15 Apr 2025 05:28:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744709288; 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=gMH03W6zuGFz+lUn3PNdcubr8mjzr75KzQr7lTep0Oc=; b=XOKpxTnY9yqZqz7sHCwN+qfdfai5+7JEOf28lEHl/VAeJBeVFtK9I6InAq8+ipnOKcl5Ts NNmleprNoBotoqMZZZEEqx6KHwjDEXKI9gn6YeN5ziweA0D5a80jKwaCntLmjD63E0VHpo njt6UGVv5GaIk2zT+t6OeHUoaqnJl7g= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-511-9fniDGqcNvuQyfsdsKHHoQ-1; Tue, 15 Apr 2025 05:28:04 -0400 X-MC-Unique: 9fniDGqcNvuQyfsdsKHHoQ-1 X-Mimecast-MFC-AGG-ID: 9fniDGqcNvuQyfsdsKHHoQ_1744709283 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A724A180AF68; Tue, 15 Apr 2025 09:28:02 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.133]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 49F8919560AD; Tue, 15 Apr 2025 09:28:00 +0000 (UTC) Date: Tue, 15 Apr 2025 10:27:56 +0100 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 v4] QIOChannelSocket: Flush zerocopy socket error queue on sendmsg failure due to ENOBUF Message-ID: References: <20250403082121.366851-1-manish.mishra@nutanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250403082121.366851-1-manish.mishra@nutanix.com> User-Agent: Mutt/2.2.13 (2024-03-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.129.124; 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_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 Thu, Apr 03, 2025 at 04:21:21AM -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. > > Signed-off-by: Manish Mishra > --- > include/io/channel-socket.h | 5 +++ > io/channel-socket.c | 74 ++++++++++++++++++++++++++++++------- > 2 files changed, 65 insertions(+), 14 deletions(-) > > 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. > > V4: > 1. Minor nit to rename s/zero_copy_flush_pending/zerocopy_flushed_once. > > diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h > index ab15577d38..2c48b972e8 100644 > --- a/include/io/channel-socket.h > +++ b/include/io/channel-socket.h > @@ -49,6 +49,11 @@ struct QIOChannelSocket { > socklen_t remoteAddrLen; > ssize_t zero_copy_queued; > ssize_t zero_copy_sent; > + /** > + * This flag indicates whether any new data was successfully sent with > + * zerocopy since the last qio_channel_socket_flush() call. > + */ > + bool new_zero_copy_sent_success; > }; > > > diff --git a/io/channel-socket.c b/io/channel-socket.c > index 608bcf066e..d5882c16fe 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 zerocopy_flushed_once = FALSE; > > 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 (!zerocopy_flushed_once) { > + ret = qio_channel_socket_flush_internal(ioc, false, errp); Passing in 'errp', so the error will be set on failure of this method... > + if (ret < 0) { > + error_setg_errno(errp, errno, > + "Zerocopy flush failed"); ...but we now try to overwrite the already set error. This error_setg_errno call should be removed. > + return -1; > + } > + zerocopy_flushed_once = TRUE; > + goto retry; > + } else { > + error_setg_errno(errp, errno, > + "Process can't lock enough memory for " > + "using MSG_ZEROCOPY"); > + return -1; > + } > } > break; > } 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 :|