From 674b892ede247ef4fb8d00918f02e29c32b9bbaf Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Tue, 16 Oct 2007 01:25:03 -0700 Subject: [PATCH] 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index ec25ba1aef5f..ca04226bf1de 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -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; -- GitLab