Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 674b892e authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

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: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8268f5a7

mm/filemap.c

+9 −2
Original line number Diff line number Diff line
@@ -2061,7 +2061,7 @@ static ssize_t generic_perform_write_2copy(struct file *file, 
		 * 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 @@ static ssize_t generic_perform_write(struct file *file, 
	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 @@ static ssize_t generic_perform_write(struct file *file, 
			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;