Avoid cache line miss dereferencing struct page if we can.
page_copy_sane() mostly deals with order-0 pages.
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Al Viro <v...@zeniv.linux.org.uk>
---
lib/iov_iter.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index
54c248526b55fc498c996f2a5ea651262fcc7f61..2a1e282c3d38e2d03b075f54b7f9313e48b90289
100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -854,8 +854,18 @@ 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;
+
+ /*
+ * Fast path if this is an order-0 page,
+ * or if the copied area fits the first page of a compound one.
+ */
+ if (likely(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;
--
2.20.0.rc2.403.gdbc3b29805-goog
