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authorEric Dumazet <edumazet@google.com>2019-02-26 10:42:39 -0800
committerAl Viro <viro@zeniv.linux.org.uk>2019-02-26 14:05:20 -0500
commit6daef95b8c914866a46247232a048447fff97279 (patch)
tree086688168650fe491deae0da957307c337bc26c5 /lib
parent77000bc43da17d5d6bc4ebfaf44d52d43bb69492 (diff)
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iov_iter: optimize page_copy_sane()
Avoid cache line miss dereferencing struct page if we can. page_copy_sane() mostly deals with order-0 pages. Extra cache line miss is visible on TCP recvmsg() calls dealing with GRO packets (typically 45 page frags are attached to one skb). Bringing the 45 struct pages into cpu cache while copying the data is not free, since the freeing of the skb (and associated page frags put_page()) can happen after cache lines have been evicted. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'lib')
-rw-r--r--lib/iov_iter.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index be4bd627caf0..ea36dc355da1 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -861,8 +861,21 @@ EXPORT_SYMBOL(_copy_from_iter_full_nocache);
static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
{
- struct page *head = compound_head(page);
- size_t v = n + offset + page_address(page) - page_address(head);
+ struct page *head;
+ size_t v = n + offset;
+
+ /*
+ * The general case needs to access the page order in order
+ * to compute the page size.
+ * However, we mostly deal with order-0 pages and thus can
+ * avoid a possible cache line miss for requests that fit all
+ * page orders.
+ */
+ if (n <= v && v <= PAGE_SIZE)
+ return true;
+
+ head = compound_head(page);
+ v += (page - head) << PAGE_SHIFT;
if (likely(n <= v && v <= (PAGE_SIZE << compound_order(head))))
return true;