| Message ID | 20230515093345.396978-4-dhowells@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | splice, net: Replace sendpage with sendmsg(MSG_SPLICE_PAGES), part 1 | expand |
On Mon, 2023-05-15 at 10:33 +0100, David Howells wrote: > Add a function to handle MSG_SPLICE_PAGES being passed internally to > sendmsg(). Pages are spliced into the given socket buffer if possible and > copied in if not (e.g. they're slab pages or have a zero refcount). > > Signed-off-by: David Howells <dhowells@redhat.com> > cc: Eric Dumazet <edumazet@google.com> > cc: "David S. Miller" <davem@davemloft.net> > cc: David Ahern <dsahern@kernel.org> > cc: Jakub Kicinski <kuba@kernel.org> > cc: Paolo Abeni <pabeni@redhat.com> > cc: Al Viro <viro@zeniv.linux.org.uk> > cc: Jens Axboe <axboe@kernel.dk> > cc: Matthew Wilcox <willy@infradead.org> > cc: netdev@vger.kernel.org > --- > > Notes: > ver #7) > - Export function. > - Never copy data, return -EIO if sendpage_ok() returns false. > > include/linux/skbuff.h | 3 ++ > net/core/skbuff.c | 95 ++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 98 insertions(+) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index 4c0ad48e38ca..1c5f0ac6f8c3 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -5097,5 +5097,8 @@ static inline void skb_mark_for_recycle(struct sk_buff *skb) > #endif > } > > +ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, > + ssize_t maxsize, gfp_t gfp); > + > #endif /* __KERNEL__ */ > #endif /* _LINUX_SKBUFF_H */ > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 7f53dcb26ad3..56d629ea2f3d 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -6892,3 +6892,98 @@ nodefer: __kfree_skb(skb); > if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1)) > smp_call_function_single_async(cpu, &sd->defer_csd); > } > + > +static void skb_splice_csum_page(struct sk_buff *skb, struct page *page, > + size_t offset, size_t len) > +{ > + const char *kaddr; > + __wsum csum; > + > + kaddr = kmap_local_page(page); > + csum = csum_partial(kaddr + offset, len, 0); > + kunmap_local(kaddr); > + skb->csum = csum_block_add(skb->csum, csum, skb->len); > +} > + > +/** > + * skb_splice_from_iter - Splice (or copy) pages to skbuff > + * @skb: The buffer to add pages to > + * @iter: Iterator representing the pages to be added > + * @maxsize: Maximum amount of pages to be added > + * @gfp: Allocation flags > + * > + * This is a common helper function for supporting MSG_SPLICE_PAGES. It > + * extracts pages from an iterator and adds them to the socket buffer if > + * possible, copying them to fragments if not possible (such as if they're slab > + * pages). > + * > + * Returns the amount of data spliced/copied or -EMSGSIZE if there's > + * insufficient space in the buffer to transfer anything. > + */ > +ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, > + ssize_t maxsize, gfp_t gfp) > +{ > + struct page *pages[8], **ppages = pages; > + unsigned int i; > + ssize_t spliced = 0, ret = 0; > + size_t frag_limit = READ_ONCE(sysctl_max_skb_frags); Minor nit: please respect the reverse x-mas tree order (there are a few other occurrences around) > + > + while (iter->count > 0) { > + ssize_t space, nr; > + size_t off, len; > + > + ret = -EMSGSIZE; > + space = frag_limit - skb_shinfo(skb)->nr_frags; > + if (space < 0) > + break; > + > + /* We might be able to coalesce without increasing nr_frags */ > + nr = clamp_t(size_t, space, 1, ARRAY_SIZE(pages)); > + > + len = iov_iter_extract_pages(iter, &ppages, maxsize, nr, 0, &off); > + if (len <= 0) { > + ret = len ?: -EIO; > + break; > + } > + > + if (space == 0 && > + !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, > + pages[0], off)) { > + iov_iter_revert(iter, len); > + break; > + } It looks like the above condition/checks duplicate what the later skb_append_pagefrags() will perform below. I guess the above chunk could be removed? > + > + i = 0; > + do { > + struct page *page = pages[i++]; > + size_t part = min_t(size_t, PAGE_SIZE - off, len); > + > + ret = -EIO; > + if (!sendpage_ok(page)) > + goto out; My (limited) understanding is that the current sendpage code assumes that the caller provides/uses pages suitable for such use. The existing sendpage_ok() check is in place as way to try to catch possible code bug - via the WARN_ONCE(). I think the same could be done here? Thanks! Paolo > + > + ret = skb_append_pagefrags(skb, page, off, part, > + frag_limit); > + if (ret < 0) { > + iov_iter_revert(iter, len); > + goto out; > + } > + > + if (skb->ip_summed == CHECKSUM_NONE) > + skb_splice_csum_page(skb, page, off, part); > + > + off = 0; > + spliced += part; > + maxsize -= part; > + len -= part; > + } while (len > 0); > + > + if (maxsize <= 0) > + break; > + } > + > +out: > + skb_len_add(skb, spliced); > + return spliced ?: ret; > +} > +EXPORT_SYMBOL(skb_splice_from_iter); >
Paolo Abeni <pabeni@redhat.com> wrote: > Minor nit: please respect the reverse x-mas tree order (there are a few > other occurrences around) I hadn't come across that. Normally I only apply that to the types so that the names aren't all over the place. But whatever. > > + if (space == 0 && > > + !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, > > + pages[0], off)) { > > + iov_iter_revert(iter, len); > > + break; > > + } > > It looks like the above condition/checks duplicate what the later > skb_append_pagefrags() will perform below. I guess the above chunk > could be removed? Good point. There used to be an allocation between in the case sendpage_ok() failed and we wanted to copy the data. I've removed that for the moment. > > + ret = -EIO; > > + if (!sendpage_ok(page)) > > + goto out; > > My (limited) understanding is that the current sendpage code assumes > that the caller provides/uses pages suitable for such use. The existing > sendpage_ok() check is in place as way to try to catch possible code > bug - via the WARN_ONCE(). > > I think the same could be done here? Yeah. Okay, I made the attached changes to this patch. David --- diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 56d629ea2f3d..f4a5b51aed22 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6923,10 +6923,10 @@ static void skb_splice_csum_page(struct sk_buff *skb, struct page *page, ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, ssize_t maxsize, gfp_t gfp) { + size_t frag_limit = READ_ONCE(sysctl_max_skb_frags); struct page *pages[8], **ppages = pages; - unsigned int i; ssize_t spliced = 0, ret = 0; - size_t frag_limit = READ_ONCE(sysctl_max_skb_frags); + unsigned int i; while (iter->count > 0) { ssize_t space, nr; @@ -6946,20 +6946,13 @@ ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, break; } - if (space == 0 && - !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, - pages[0], off)) { - iov_iter_revert(iter, len); - break; - } - i = 0; do { struct page *page = pages[i++]; size_t part = min_t(size_t, PAGE_SIZE - off, len); ret = -EIO; - if (!sendpage_ok(page)) + if (WARN_ON_ONCE(!sendpage_ok(page))) goto out; ret = skb_append_pagefrags(skb, page, off, part,
On Thu, 2023-05-18 at 10:53 +0100, David Howells wrote: > Paolo Abeni <pabeni@redhat.com> wrote: > > > Minor nit: please respect the reverse x-mas tree order (there are a few > > other occurrences around) > > I hadn't come across that. Normally I only apply that to the types so that > the names aren't all over the place. But whatever. > > > > + if (space == 0 && > > > + !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, > > > + pages[0], off)) { > > > + iov_iter_revert(iter, len); > > > + break; > > > + } > > > > It looks like the above condition/checks duplicate what the later > > skb_append_pagefrags() will perform below. I guess the above chunk > > could be removed? > > Good point. There used to be an allocation between in the case sendpage_ok() > failed and we wanted to copy the data. I've removed that for the moment. > > > > + ret = -EIO; > > > + if (!sendpage_ok(page)) > > > + goto out; > > > > My (limited) understanding is that the current sendpage code assumes > > that the caller provides/uses pages suitable for such use. The existing > > sendpage_ok() check is in place as way to try to catch possible code > > bug - via the WARN_ONCE(). > > > > I think the same could be done here? > > Yeah. > > Okay, I made the attached changes to this patch. > > David > --- > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 56d629ea2f3d..f4a5b51aed22 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -6923,10 +6923,10 @@ static void skb_splice_csum_page(struct sk_buff *skb, struct page *page, > ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, > ssize_t maxsize, gfp_t gfp) > { > + size_t frag_limit = READ_ONCE(sysctl_max_skb_frags); > struct page *pages[8], **ppages = pages; > - unsigned int i; > ssize_t spliced = 0, ret = 0; > - size_t frag_limit = READ_ONCE(sysctl_max_skb_frags); > + unsigned int i; > > while (iter->count > 0) { > ssize_t space, nr; > @@ -6946,20 +6946,13 @@ ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, > break; > } > > - if (space == 0 && > - !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, > - pages[0], off)) { > - iov_iter_revert(iter, len); > - break; > - } > - > i = 0; > do { > struct page *page = pages[i++]; > size_t part = min_t(size_t, PAGE_SIZE - off, len); > > ret = -EIO; > - if (!sendpage_ok(page)) > + if (WARN_ON_ONCE(!sendpage_ok(page))) FWIS the current TCP code also has a 'IS_ENABLED(CONFIG_DEBUG_VM) &&' guard, but I guess the plain WARN_ON_ONCE should be ok. Side node: we need the whole series alltogether, you need to repost even the unmodified patches. Thanks! Paolo
Paolo Abeni <pabeni@redhat.com> wrote: > Side node: we need the whole series alltogether, you need to repost > even the unmodified patches. Any other things to change before I do that? David
On Thu, 2023-05-18 at 11:32 +0100, David Howells wrote: > Paolo Abeni <pabeni@redhat.com> wrote: > > > Side node: we need the whole series alltogether, you need to repost > > even the unmodified patches. > > Any other things to change before I do that? I went through the series and don't have other comments. Cheers, Paolo
Paolo Abeni <pabeni@redhat.com> wrote: > > Any other things to change before I do that? > > I went through the series and don't have other comments. Thanks! David
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 4c0ad48e38ca..1c5f0ac6f8c3 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -5097,5 +5097,8 @@ static inline void skb_mark_for_recycle(struct sk_buff *skb) #endif } +ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, + ssize_t maxsize, gfp_t gfp); + #endif /* __KERNEL__ */ #endif /* _LINUX_SKBUFF_H */ diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 7f53dcb26ad3..56d629ea2f3d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6892,3 +6892,98 @@ nodefer: __kfree_skb(skb); if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1)) smp_call_function_single_async(cpu, &sd->defer_csd); } + +static void skb_splice_csum_page(struct sk_buff *skb, struct page *page, + size_t offset, size_t len) +{ + const char *kaddr; + __wsum csum; + + kaddr = kmap_local_page(page); + csum = csum_partial(kaddr + offset, len, 0); + kunmap_local(kaddr); + skb->csum = csum_block_add(skb->csum, csum, skb->len); +} + +/** + * skb_splice_from_iter - Splice (or copy) pages to skbuff + * @skb: The buffer to add pages to + * @iter: Iterator representing the pages to be added + * @maxsize: Maximum amount of pages to be added + * @gfp: Allocation flags + * + * This is a common helper function for supporting MSG_SPLICE_PAGES. It + * extracts pages from an iterator and adds them to the socket buffer if + * possible, copying them to fragments if not possible (such as if they're slab + * pages). + * + * Returns the amount of data spliced/copied or -EMSGSIZE if there's + * insufficient space in the buffer to transfer anything. + */ +ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, + ssize_t maxsize, gfp_t gfp) +{ + struct page *pages[8], **ppages = pages; + unsigned int i; + ssize_t spliced = 0, ret = 0; + size_t frag_limit = READ_ONCE(sysctl_max_skb_frags); + + while (iter->count > 0) { + ssize_t space, nr; + size_t off, len; + + ret = -EMSGSIZE; + space = frag_limit - skb_shinfo(skb)->nr_frags; + if (space < 0) + break; + + /* We might be able to coalesce without increasing nr_frags */ + nr = clamp_t(size_t, space, 1, ARRAY_SIZE(pages)); + + len = iov_iter_extract_pages(iter, &ppages, maxsize, nr, 0, &off); + if (len <= 0) { + ret = len ?: -EIO; + break; + } + + if (space == 0 && + !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, + pages[0], off)) { + iov_iter_revert(iter, len); + break; + } + + i = 0; + do { + struct page *page = pages[i++]; + size_t part = min_t(size_t, PAGE_SIZE - off, len); + + ret = -EIO; + if (!sendpage_ok(page)) + goto out; + + ret = skb_append_pagefrags(skb, page, off, part, + frag_limit); + if (ret < 0) { + iov_iter_revert(iter, len); + goto out; + } + + if (skb->ip_summed == CHECKSUM_NONE) + skb_splice_csum_page(skb, page, off, part); + + off = 0; + spliced += part; + maxsize -= part; + len -= part; + } while (len > 0); + + if (maxsize <= 0) + break; + } + +out: + skb_len_add(skb, spliced); + return spliced ?: ret; +} +EXPORT_SYMBOL(skb_splice_from_iter);
Add a function to handle MSG_SPLICE_PAGES being passed internally to sendmsg(). Pages are spliced into the given socket buffer if possible and copied in if not (e.g. they're slab pages or have a zero refcount). Signed-off-by: David Howells <dhowells@redhat.com> cc: Eric Dumazet <edumazet@google.com> cc: "David S. Miller" <davem@davemloft.net> cc: David Ahern <dsahern@kernel.org> cc: Jakub Kicinski <kuba@kernel.org> cc: Paolo Abeni <pabeni@redhat.com> cc: Al Viro <viro@zeniv.linux.org.uk> cc: Jens Axboe <axboe@kernel.dk> cc: Matthew Wilcox <willy@infradead.org> cc: netdev@vger.kernel.org --- Notes: ver #7) - Export function. - Never copy data, return -EIO if sendpage_ok() returns false. include/linux/skbuff.h | 3 ++ net/core/skbuff.c | 95 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 98 insertions(+)