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-rw-r--r--mm/shmem.c31
1 files changed, 20 insertions, 11 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 529c9ad3e926..4b2fea33158e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2513,7 +2513,6 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
pgoff_t end_index;
unsigned long nr, ret;
loff_t i_size = i_size_read(inode);
- bool got_page;
end_index = i_size >> PAGE_SHIFT;
if (index > end_index)
@@ -2570,24 +2569,34 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
*/
if (!offset)
mark_page_accessed(page);
- got_page = true;
+ /*
+ * Ok, we have the page, and it's up-to-date, so
+ * now we can copy it to user space...
+ */
+ ret = copy_page_to_iter(page, offset, nr, to);
+ put_page(page);
+
+ } else if (iter_is_iovec(to)) {
+ /*
+ * Copy to user tends to be so well optimized, but
+ * clear_user() not so much, that it is noticeably
+ * faster to copy the zero page instead of clearing.
+ */
+ ret = copy_page_to_iter(ZERO_PAGE(0), offset, nr, to);
} else {
- page = ZERO_PAGE(0);
- got_page = false;
+ /*
+ * But submitting the same page twice in a row to
+ * splice() - or others? - can result in confusion:
+ * so don't attempt that optimization on pipes etc.
+ */
+ ret = iov_iter_zero(nr, to);
}
- /*
- * Ok, we have the page, and it's up-to-date, so
- * now we can copy it to user space...
- */
- ret = copy_page_to_iter(page, offset, nr, to);
retval += ret;
offset += ret;
index += offset >> PAGE_SHIFT;
offset &= ~PAGE_MASK;
- if (got_page)
- put_page(page);
if (!iov_iter_count(to))
break;
if (ret < nr) {