mm: restore KERNEL_DS optimisations
Restore the KERNEL_DS optimisation, especially helpful to the 2copy write
path.
This may be a pretty questionable gain in most cases, especially after the
legacy 2copy write path is removed, but it doesn't cost much.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap.c b/mm/filemap.c
index ec25ba1..ca04226 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2061,7 +2061,7 @@
* cannot take a pagefault with the destination page locked.
* So pin the source page to copy it.
*/
- if (!PageUptodate(page)) {
+ if (!PageUptodate(page) && !segment_eq(get_fs(), KERNEL_DS)) {
unlock_page(page);
src_page = alloc_page(GFP_KERNEL);
@@ -2186,6 +2186,13 @@
const struct address_space_operations *a_ops = mapping->a_ops;
long status = 0;
ssize_t written = 0;
+ unsigned int flags = 0;
+
+ /*
+ * Copies from kernel address space cannot fail (NFSD is a big user).
+ */
+ if (segment_eq(get_fs(), KERNEL_DS))
+ flags |= AOP_FLAG_UNINTERRUPTIBLE;
do {
struct page *page;
@@ -2217,7 +2224,7 @@
break;
}
- status = a_ops->write_begin(file, mapping, pos, bytes, 0,
+ status = a_ops->write_begin(file, mapping, pos, bytes, flags,
&page, &fsdata);
if (unlikely(status))
break;