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mm: restore KERNEL_DS optimisations

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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>
This commit is contained in:
Nick Piggin 2007-10-16 01:25:03 -07:00 committed by Linus Torvalds
parent 8268f5a741
commit 674b892ede
1 changed files with 9 additions and 2 deletions
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11
mm/filemap.c
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@ -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 @@ 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;