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envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=148.163.155.12; envelope-from=tejus.gk@nutanix.com; helo=mx0b-002c1b01.pphosted.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.442, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=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: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @nutanix.com) X-ZM-MESSAGEID: 1760004979827154100 Content-Type: text/plain; charset="utf-8" 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 | 78 ++++++++++++++++++++++++++++++------- migration/multifd-nocomp.c | 3 +- migration/multifd.c | 3 +- 4 files changed, 72 insertions(+), 17 deletions(-) diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h index 26319fa98b..fcfd489c6c 100644 --- a/include/io/channel-socket.h +++ b/include/io/channel-socket.h @@ -50,6 +50,11 @@ struct QIOChannelSocket { ssize_t zero_copy_queued; ssize_t zero_copy_sent; bool blocking; + /** + * 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; }; =20 =20 diff --git a/io/channel-socket.c b/io/channel-socket.c index 8b30d5b7f7..22d59cd3cf 100644 --- a/io/channel-socket.c +++ b/io/channel-socket.c @@ -37,6 +37,12 @@ =20 #define SOCKET_MAX_FDS 16 =20 +#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) @@ -66,6 +72,7 @@ qio_channel_socket_new(void) sioc->zero_copy_queued =3D 0; sioc->zero_copy_sent =3D 0; sioc->blocking =3D false; + sioc->new_zero_copy_sent_success =3D FALSE; =20 ioc =3D QIO_CHANNEL(sioc); qio_channel_set_feature(ioc, QIO_CHANNEL_FEATURE_SHUTDOWN); @@ -618,6 +625,8 @@ static ssize_t qio_channel_socket_writev(QIOChannel *io= c, size_t fdsize =3D sizeof(int) * nfds; struct cmsghdr *cmsg; int sflags =3D 0; + bool blocking =3D sioc->blocking; + bool zerocopy_flushed_once =3D false; =20 memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS)); =20 @@ -663,10 +672,26 @@ static ssize_t qio_channel_socket_writev(QIOChannel *= ioc, case EINTR: goto retry; case ENOBUFS: - if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) { - error_setg_errno(errp, errno, - "Process can't lock enough memory for usi= ng MSG_ZEROCOPY"); - return -1; + if (flags & (QIO_CHANNEL_WRITE_FLAG_ZERO_COPY | + QIO_CHANNEL_WRITE_FLAG_ZERO_COPY_FLUSH_ONCE)) { + /** + * Socket error queueing may exhaust the OPTMEM limit. Try + * flushing the error queue once. + */ + if (!zerocopy_flushed_once) { + ret =3D qio_channel_socket_flush_internal(ioc, blockin= g, + errp); + if (ret < 0) { + return -1; + } + zerocopy_flushed_once =3D TRUE; + goto retry; + } else { + error_setg_errno(errp, errno, + "Process can't lock enough memory for= " + "using MSG_ZEROCOPY"); + return -1; + } } break; } @@ -777,8 +802,9 @@ static ssize_t qio_channel_socket_writev(QIOChannel *io= c, =20 =20 #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 =3D QIO_CHANNEL_SOCKET(ioc); struct msghdr msg =3D {}; @@ -786,7 +812,6 @@ static int qio_channel_socket_flush(QIOChannel *ioc, struct cmsghdr *cm; char control[CMSG_SPACE(sizeof(*serr))]; int received; - int ret; =20 if (sioc->zero_copy_queued =3D=3D sioc->zero_copy_sent) { return 0; @@ -796,16 +821,20 @@ static int qio_channel_socket_flush(QIOChannel *ioc, msg.msg_controllen =3D sizeof(control); memset(control, 0, sizeof(control)); =20 - ret =3D 1; - while (sioc->zero_copy_sent < sioc->zero_copy_queued) { received =3D 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: @@ -843,13 +872,32 @@ static int qio_channel_socket_flush(QIOChannel *ioc, /* No errors, count successfully finished sendmsg()*/ sioc->zero_copy_sent +=3D serr->ee_data - serr->ee_info + 1; =20 - /* If any sendmsg() succeeded using zero copy, return 0 at the end= */ + /* If any sendmsg() succeeded using zero copy, mark zerocopy succe= ss */ if (serr->ee_code !=3D SO_EE_CODE_ZEROCOPY_COPIED) { - ret =3D 0; + sioc->new_zero_copy_sent_success =3D TRUE; } } =20 - return ret; + return 0; +} + +static int qio_channel_socket_flush(QIOChannel *ioc, + Error **errp) +{ + QIOChannelSocket *sioc =3D QIO_CHANNEL_SOCKET(ioc); + int ret; + + ret =3D 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 =3D FALSE; + return 0; + } + + return 1; } =20 #endif /* QEMU_MSG_ZEROCOPY */ diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c index b48eae3d86..9a28ccafd6 100644 --- a/migration/multifd-nocomp.c +++ b/migration/multifd-nocomp.c @@ -66,7 +66,8 @@ static int multifd_nocomp_send_setup(MultiFDSendParams *p= , Error **errp) uint32_t page_count =3D multifd_ram_page_count(); =20 if (migrate_zero_copy_send()) { - p->write_flags |=3D QIO_CHANNEL_WRITE_FLAG_ZERO_COPY; + p->write_flags |=3D (QIO_CHANNEL_WRITE_FLAG_ZERO_COPY | + QIO_CHANNEL_WRITE_FLAG_ZERO_COPY_FLUSH_ONCE); } =20 if (!migrate_mapped_ram()) { diff --git a/migration/multifd.c b/migration/multifd.c index 98873cee74..ccfafa6505 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -703,7 +703,8 @@ static void *multifd_send_thread(void *opaque) multifd_device_state_send_prepare(p); =20 /* Device state packets cannot be sent via zerocopy */ - write_flags_masked |=3D QIO_CHANNEL_WRITE_FLAG_ZERO_COPY; + write_flags_masked |=3D (QIO_CHANNEL_WRITE_FLAG_ZERO_COPY | + QIO_CHANNEL_WRITE_FLAG_ZERO_COPY_FLUSH_ONCE); } else { ret =3D multifd_send_state->ops->send_prepare(p, &local_er= r); if (ret !=3D 0) { --=20 2.43.7