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Wysocki" , Len Brown , Vivek Goyal , Keith Busch Message-ID: <2089367516.35808121.1574323316486.JavaMail.zimbra@redhat.com> In-Reply-To: References: <20191120092831.6198-1-pagupta@redhat.com> Subject: Re: [PATCH] virtio pmem: fix async flush ordering MIME-Version: 1.0 X-Originating-IP: [10.67.116.169, 10.4.195.1] Thread-Topic: virtio pmem: fix async flush ordering Thread-Index: n73vjZWQN2B3un3TvjjmhkQyzbgvzg== X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: g80Ev-2mMmmrw3oAT5So1Q-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > > > Remove logic to create child bio in the async flush function which > > > causes child bio to get executed after parent bio 'pmem_make_request= ' > > > completes. This resulted in wrong ordering of REQ_PREFLUSH with the > > > data write request. > > > > > > Instead we are performing flush from the parent bio to maintain the > > > correct order. Also, returning from function 'pmem_make_request' if > > > REQ_PREFLUSH returns an error. > > > > > > Reported-by: Jeff Moyer > > > Signed-off-by: Pankaj Gupta > > > > There's a slight change in behavior for the error path in the > > virtio_pmem driver. Previously, all errors from virtio_pmem_flush were > > converted to -EIO. Now, they are reported as-is. I think this is > > actually an improvement. > > > > I'll also note that the current behavior can result in data corruption, > > so this should be tagged for stable. >=20 > I added that and was about to push this out, but what about the fact > that now the guest will synchronously wait for flushing to occur. The > goal of the child bio was to allow that to be an I/O wait with > overlapping I/O, or at least not blocking the submission thread. Does > the block layer synchronously wait for PREFLUSH requests? If not I > think a synchronous wait is going to be a significant performance > regression. Are there any numbers to accompany this change? My bad, I missed this point completely. Thanks, Pankaj >=20 >=20