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Message-Id: <597c7c76624997d8933740e74e9b82d026bcfeff.1653992701.git.asml.silence@gmail.com>
Date: Tue, 28 Jun 2022 19:56:28 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: io-uring@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Jonathan Lemon <jonathan.lemon@...il.com>,
Willem de Bruijn <willemb@...gle.com>,
Jens Axboe <axboe@...nel.dk>, kernel-team@...com,
Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC net-next v3 06/29] net: optimise bvec-based zc page referencing
Some users like io_uring can pass a bvec iterator to send and also can
implement page pinning more efficiently. Add a ->msg_managed_data toogle
in msghdr. When set, data pages are "managed" by upper layers, i.e.
refcounted and pinned by the caller and will live at least until
->msg_ubuf is released. msghdr has to have non-NULL ->msg_ubuf and
->msg_iter should point to a bvec.
Protocols supporting the feature will propagate it by setting
SKBFL_MANAGED_FRAG_REFS, which means that the skb doesn't hold refs to
its frag pages and only rely on ubuf_info lifetime gurantees. It should
only be used with zerocopy skbs with ubuf_info set.
It's allowed to convert skbs from managed to normal by calling
skb_zcopy_downgrade_managed(). The function will take all needed
page references and clear the flag.
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
include/linux/skbuff.h | 25 +++++++++++++++++++++++--
net/core/datagram.c | 7 ++++---
net/core/skbuff.c | 29 +++++++++++++++++++++++++++--
3 files changed, 54 insertions(+), 7 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index eead3527bdaf..5407cfd9cb89 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -688,11 +688,16 @@ enum {
SKBFL_PURE_ZEROCOPY = BIT(2),
SKBFL_DONT_ORPHAN = BIT(3),
+
+ /* page references are managed by the ubuf_info, so it's safe to
+ * use frags only up until ubuf_info is released
+ */
+ SKBFL_MANAGED_FRAG_REFS = BIT(4),
};
#define SKBFL_ZEROCOPY_FRAG (SKBFL_ZEROCOPY_ENABLE | SKBFL_SHARED_FRAG)
#define SKBFL_ALL_ZEROCOPY (SKBFL_ZEROCOPY_FRAG | SKBFL_PURE_ZEROCOPY | \
- SKBFL_DONT_ORPHAN)
+ SKBFL_DONT_ORPHAN | SKBFL_MANAGED_FRAG_REFS)
/*
* The callback notifies userspace to release buffers when skb DMA is done in
@@ -1809,6 +1814,11 @@ static inline bool skb_zcopy_pure(const struct sk_buff *skb)
return skb_shinfo(skb)->flags & SKBFL_PURE_ZEROCOPY;
}
+static inline bool skb_zcopy_managed(const struct sk_buff *skb)
+{
+ return skb_shinfo(skb)->flags & SKBFL_MANAGED_FRAG_REFS;
+}
+
static inline bool skb_pure_zcopy_same(const struct sk_buff *skb1,
const struct sk_buff *skb2)
{
@@ -1883,6 +1893,14 @@ static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy_success)
}
}
+void __skb_zcopy_downgrade_managed(struct sk_buff *skb);
+
+static inline void skb_zcopy_downgrade_managed(struct sk_buff *skb)
+{
+ if (unlikely(skb_zcopy_managed(skb)))
+ __skb_zcopy_downgrade_managed(skb);
+}
+
static inline void skb_mark_not_on_list(struct sk_buff *skb)
{
skb->next = NULL;
@@ -3491,7 +3509,10 @@ static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle)
*/
static inline void skb_frag_unref(struct sk_buff *skb, int f)
{
- __skb_frag_unref(&skb_shinfo(skb)->frags[f], skb->pp_recycle);
+ struct skb_shared_info *shinfo = skb_shinfo(skb);
+
+ if (!skb_zcopy_managed(skb))
+ __skb_frag_unref(&shinfo->frags[f], skb->pp_recycle);
}
/**
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 5237cb533bb4..a93c05156f56 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -631,7 +631,6 @@ static int __zerocopy_sg_from_bvec(struct sock *sk, struct sk_buff *skb,
copied += v.bv_len;
truesize += PAGE_ALIGN(v.bv_len + v.bv_offset);
- get_page(v.bv_page);
skb_fill_page_desc(skb, frag++, v.bv_page, v.bv_offset, v.bv_len);
bvec_iter_advance_single(from->bvec, &bi, v.bv_len);
}
@@ -660,11 +659,13 @@ static int __zerocopy_sg_from_bvec(struct sock *sk, struct sk_buff *skb,
int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
struct iov_iter *from, size_t length)
{
- int frag = skb_shinfo(skb)->nr_frags;
+ int frag;
- if (iov_iter_is_bvec(from))
+ if (skb_zcopy_managed(skb))
return __zerocopy_sg_from_bvec(sk, skb, from, length);
+ frag = skb_shinfo(skb)->nr_frags;
+
while (length && iov_iter_count(from)) {
struct page *pages[MAX_SKB_FRAGS];
struct page *last_head = NULL;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5b35791064d1..71870def129c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -666,11 +666,18 @@ static void skb_release_data(struct sk_buff *skb)
&shinfo->dataref))
goto exit;
- skb_zcopy_clear(skb, true);
+ if (skb_zcopy(skb)) {
+ bool skip_unref = shinfo->flags & SKBFL_MANAGED_FRAG_REFS;
+
+ skb_zcopy_clear(skb, true);
+ if (skip_unref)
+ goto free_head;
+ }
for (i = 0; i < shinfo->nr_frags; i++)
__skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);
+free_head:
if (shinfo->frag_list)
kfree_skb_list(shinfo->frag_list);
@@ -895,7 +902,10 @@ EXPORT_SYMBOL(skb_dump);
*/
void skb_tx_error(struct sk_buff *skb)
{
- skb_zcopy_clear(skb, true);
+ if (skb) {
+ skb_zcopy_downgrade_managed(skb);
+ skb_zcopy_clear(skb, true);
+ }
}
EXPORT_SYMBOL(skb_tx_error);
@@ -1371,6 +1381,16 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
}
EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);
+void __skb_zcopy_downgrade_managed(struct sk_buff *skb)
+{
+ int i;
+
+ skb_shinfo(skb)->flags &= ~SKBFL_MANAGED_FRAG_REFS;
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
+ skb_frag_ref(skb, i);
+}
+EXPORT_SYMBOL_GPL(__skb_zcopy_downgrade_managed);
+
static int skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig,
gfp_t gfp_mask)
{
@@ -1688,6 +1708,8 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
BUG_ON(skb_shared(skb));
+ skb_zcopy_downgrade_managed(skb);
+
size = SKB_DATA_ALIGN(size);
if (skb_pfmemalloc(skb))
@@ -3484,6 +3506,8 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len)
int pos = skb_headlen(skb);
const int zc_flags = SKBFL_SHARED_FRAG | SKBFL_PURE_ZEROCOPY;
+ skb_zcopy_downgrade_managed(skb);
+
skb_shinfo(skb1)->flags |= skb_shinfo(skb)->flags & zc_flags;
skb_zerocopy_clone(skb1, skb, 0);
if (len < pos) /* Split line is inside header. */
@@ -3837,6 +3861,7 @@ int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
if (skb_can_coalesce(skb, i, page, offset)) {
skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size);
} else if (i < MAX_SKB_FRAGS) {
+ skb_zcopy_downgrade_managed(skb);
get_page(page);
skb_fill_page_desc(skb, i, page, offset, size);
} else {
--
2.36.1
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