| Message ID | 20230331160914.1608208-42-dhowells@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | splice, net: Replace sendpage with sendmsg(MSG_SPLICE_PAGES) | expand |
On venerdì 31 marzo 2023 18:09:00 CEST David Howells wrote: > As iscsi is now using sendmsg() with MSG_SPLICE_PAGES rather than sendpage, > assume that sendpage_ok() will return true in iscsi_tcp_segment_map() and > leave it to TCP to copy the data if not. > > Signed-off-by: David Howells <dhowells@redhat.com> > cc: "Martin K. Petersen" <martin.petersen@oracle.com> > cc: "David S. Miller" <davem@davemloft.net> > cc: Eric Dumazet <edumazet@google.com> > cc: Jakub Kicinski <kuba@kernel.org> > cc: Paolo Abeni <pabeni@redhat.com> > cc: Jens Axboe <axboe@kernel.dk> > cc: Matthew Wilcox <willy@infradead.org> > cc: linux-scsi@vger.kernel.org > cc: target-devel@vger.kernel.org > cc: netdev@vger.kernel.org > --- > drivers/scsi/libiscsi_tcp.c | 13 +++---------- > 1 file changed, 3 insertions(+), 10 deletions(-) > > diff --git a/drivers/scsi/libiscsi_tcp.c b/drivers/scsi/libiscsi_tcp.c > index c182aa83f2c9..07ba0d864820 100644 > --- a/drivers/scsi/libiscsi_tcp.c > +++ b/drivers/scsi/libiscsi_tcp.c > @@ -128,18 +128,11 @@ static void iscsi_tcp_segment_map(struct iscsi_segment > *segment, int recv) * coalescing neighboring slab objects into a single frag > which > * triggers one of hardened usercopy checks. > */ > - if (!recv && sendpage_ok(sg_page(sg))) > + if (!recv) > return; > > - if (recv) { > - segment->atomic_mapped = true; > - segment->sg_mapped = kmap_atomic(sg_page(sg)); > - } else { > - segment->atomic_mapped = false; > - /* the xmit path can sleep with the page mapped so use kmap */ > - segment->sg_mapped = kmap(sg_page(sg)); > - } > - > + segment->atomic_mapped = true; > + segment->sg_mapped = kmap_atomic(sg_page(sg)); As you probably know, kmap_atomic() is deprecated. I must admit that I'm not an expert of this code, however, it looks like the mapping has no need to rely on the side effects of kmap_atomic() (i.e., pagefault_disable() and preempt_disable() - but I'm not entirely sure about the possibility that preemption should be explicitly disabled along with the replacement with kmap_local_page()). Last year I've been working on several conversions from kmap{,_atomic}() to kmap_local_page(), however I'm still not sure to understand what's happening here... Am I missing any important details? Can you please explain why we still need that kmap_atomic() instead of kmap_local_page()? Thanks in advance, Fabio > segment->data = segment->sg_mapped + sg->offset + segment- >sg_offset; > }
Fabio M. De Francesco <fmdefrancesco@gmail.com> wrote: > > - if (recv) { > > - segment->atomic_mapped = true; > > - segment->sg_mapped = kmap_atomic(sg_page(sg)); > > - } else { > > - segment->atomic_mapped = false; > > - /* the xmit path can sleep with the page mapped so use > kmap */ > > - segment->sg_mapped = kmap(sg_page(sg)); > > - } > > - > > + segment->atomic_mapped = true; > > + segment->sg_mapped = kmap_atomic(sg_page(sg)); > > As you probably know, kmap_atomic() is deprecated. > > I must admit that I'm not an expert of this code, however, it looks like the > mapping has no need to rely on the side effects of kmap_atomic() (i.e., > pagefault_disable() and preempt_disable() - but I'm not entirely sure about > the possibility that preemption should be explicitly disabled along with the > replacement with kmap_local_page()). > > Last year I've been working on several conversions from kmap{,_atomic}() to > kmap_local_page(), however I'm still not sure to understand what's happening > here... > > Am I missing any important details? Can you please explain why we still need > that kmap_atomic() instead of kmap_local_page()? Actually, it might be worth dropping segment->sg_mapped and segment->data and only doing the kmap_local when necessary. And this: struct msghdr msg = { .msg_flags = flags }; struct kvec iov = { .iov_base = segment->data + offset, .iov_len = copy }; r = kernel_sendmsg(sk, &msg, &iov, 1, copy); should really be using struct bvec, not struct kvec - then the mapping isn't necessary. It looks like this might be the only place the mapping is used, but I'm not 100% certain. David
On martedì 25 aprile 2023 10:30:30 CEST David Howells wrote: > Fabio M. De Francesco <fmdefrancesco@gmail.com> wrote: > > > - if (recv) { > > > - segment->atomic_mapped = true; > > > - segment->sg_mapped = kmap_atomic(sg_page(sg)); > > > - } else { > > > - segment->atomic_mapped = false; > > > - /* the xmit path can sleep with the page mapped so use > > > > kmap */ > > > > > - segment->sg_mapped = kmap(sg_page(sg)); > > > - } > > > - > > > + segment->atomic_mapped = true; > > > + segment->sg_mapped = kmap_atomic(sg_page(sg)); > > > > As you probably know, kmap_atomic() is deprecated. > > > > I must admit that I'm not an expert of this code, however, it looks like the > > mapping has no need to rely on the side effects of kmap_atomic() (i.e., > > pagefault_disable() and preempt_disable() - but I'm not entirely sure about > > the possibility that preemption should be explicitly disabled along with the > > replacement with kmap_local_page()). > > > > Last year I've been working on several conversions from kmap{,_atomic}() to > > kmap_local_page(), however I'm still not sure to understand what's happening > > here... > > > > Am I missing any important details? Can you please explain why we still need > > that kmap_atomic() instead of kmap_local_page()? > > Actually, it might be worth dropping segment->sg_mapped and segment->data and > only doing the kmap_local when necessary. > > And this: > > struct msghdr msg = { .msg_flags = flags }; > struct kvec iov = { > .iov_base = segment->data + offset, > .iov_len = copy > }; > > r = kernel_sendmsg(sk, &msg, &iov, 1, copy); > > should really be using struct bvec, not struct kvec - then the mapping isn't > necessary. FWIW, struct bvec looks better suited (despite I have very little knowledge of this code). I assume that you noticed that we also have the unmapping counterpart (iscsi_tcp_segment_unmap()) which should also be addressed accordingly. > It looks like this might be the only place the mapping is used, > but I'm not 100% certain. It seems that kmap_atomic() (as well as kmap(), which you deleted) is only called by iscsi_tcp_segment_map(), which in turn is called only by iscsi_tcp_segment_done(). I can't see any other places where the mapping is used. I hope that this dialogue may help you somehow to choose the best suited way to get rid of that deprecated kmap_atomic(). Thanks for taking time to address questions from newcomers :-) Fabio > > David
diff --git a/drivers/scsi/libiscsi_tcp.c b/drivers/scsi/libiscsi_tcp.c index c182aa83f2c9..07ba0d864820 100644 --- a/drivers/scsi/libiscsi_tcp.c +++ b/drivers/scsi/libiscsi_tcp.c @@ -128,18 +128,11 @@ static void iscsi_tcp_segment_map(struct iscsi_segment *segment, int recv) * coalescing neighboring slab objects into a single frag which * triggers one of hardened usercopy checks. */ - if (!recv && sendpage_ok(sg_page(sg))) + if (!recv) return; - if (recv) { - segment->atomic_mapped = true; - segment->sg_mapped = kmap_atomic(sg_page(sg)); - } else { - segment->atomic_mapped = false; - /* the xmit path can sleep with the page mapped so use kmap */ - segment->sg_mapped = kmap(sg_page(sg)); - } - + segment->atomic_mapped = true; + segment->sg_mapped = kmap_atomic(sg_page(sg)); segment->data = segment->sg_mapped + sg->offset + segment->sg_offset; }
As iscsi is now using sendmsg() with MSG_SPLICE_PAGES rather than sendpage, assume that sendpage_ok() will return true in iscsi_tcp_segment_map() and leave it to TCP to copy the data if not. Signed-off-by: David Howells <dhowells@redhat.com> cc: "Martin K. Petersen" <martin.petersen@oracle.com> cc: "David S. Miller" <davem@davemloft.net> cc: Eric Dumazet <edumazet@google.com> cc: Jakub Kicinski <kuba@kernel.org> cc: Paolo Abeni <pabeni@redhat.com> cc: Jens Axboe <axboe@kernel.dk> cc: Matthew Wilcox <willy@infradead.org> cc: linux-scsi@vger.kernel.org cc: target-devel@vger.kernel.org cc: netdev@vger.kernel.org --- drivers/scsi/libiscsi_tcp.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-)