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.
Cc: Linux Memory Management <linux-mm@xxxxxxxxx>
Cc: Linux Filesystems <linux-fsdevel@xxxxxxxxxxxxxxx>
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
mm/filemap.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -2123,7 +2123,7 @@ static ssize_t generic_perform_write_2co
* 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);
@@ -2248,6 +2248,13 @@ static ssize_t generic_perform_write(str
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;
@@ -2279,7 +2286,7 @@ again:
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;
--
-
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