diff options
| -rw-r--r-- | mm/filemap.c | 32 |
1 files changed, 19 insertions, 13 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 00414849a867..d1060b8d3cd6 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2079,21 +2079,27 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, /* Limit the size of the copy to the caller's write size */ bytes = min(bytes, count); - /* - * Limit the size of the copy to that of the current segment, - * because fault_in_pages_readable() doesn't know how to walk - * segments. + /* We only need to worry about prefaulting when writes are from + * user-space. NFSd uses vfs_writev with several non-aligned + * segments in the vector, and limiting to one segment a time is + * a noticeable performance for re-write */ - bytes = min(bytes, cur_iov->iov_len - iov_base); - - /* - * Bring in the user page that we will copy from _first_. - * Otherwise there's a nasty deadlock on copying from the - * same page as we're writing to, without it being marked - * up-to-date. - */ - fault_in_pages_readable(buf, bytes); + if (!segment_eq(get_fs(), KERNEL_DS)) { + /* + * Limit the size of the copy to that of the current + * segment, because fault_in_pages_readable() doesn't + * know how to walk segments. + */ + bytes = min(bytes, cur_iov->iov_len - iov_base); + /* + * Bring in the user page that we will copy from + * _first_. Otherwise there's a nasty deadlock on + * copying from the same page as we're writing to, + * without it being marked up-to-date. + */ + fault_in_pages_readable(buf, bytes); + } page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec); if (!page) { status = -ENOMEM; |