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Commit bc40d73c authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

splice: use get_user_pages_fast 



Use get_user_pages_fast in splice.  This reverts some mmap_sem batching
there, however the biggest problem with mmap_sem tends to be hold times
blocking out other threads rather than cacheline bouncing.  Further: on
architectures that implement get_user_pages_fast without locks, mmap_sem
can be avoided completely anyway.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Reviewed-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f5dd33c4

fs/splice.c

+3 −38
Original line number Diff line number Diff line
@@ -1160,36 +1160,6 @@ static long do_splice(struct file *in, loff_t __user *off_in, 
	return -EINVAL;

}



/*

 * Do a copy-from-user while holding the mmap_semaphore for reading, in a

 * manner safe from deadlocking with simultaneous mmap() (grabbing mmap_sem

 * for writing) and page faulting on the user memory pointed to by src.

 * This assumes that we will very rarely hit the partial != 0 path, or this

 * will not be a win.

 */

static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)

{

	int partial;



	if (!access_ok(VERIFY_READ, src, n))

		return -EFAULT;



	pagefault_disable();

	partial = __copy_from_user_inatomic(dst, src, n);

	pagefault_enable();



	/*

	 * Didn't copy everything, drop the mmap_sem and do a faulting copy

	 */

	if (unlikely(partial)) {

		up_read(&current->mm->mmap_sem);

		partial = copy_from_user(dst, src, n);

		down_read(&current->mm->mmap_sem);

	}



	return partial;

}



/*

 * Map an iov into an array of pages and offset/length tupples. With the

 * partial_page structure, we can map several non-contiguous ranges into
@@ -1203,8 +1173,6 @@ static int get_iovec_page_array(const struct iovec __user *iov, 
{

	int buffers = 0, error = 0;



	down_read(&current->mm->mmap_sem);



	while (nr_vecs) {

		unsigned long off, npages;

		struct iovec entry;
@@ -1213,7 +1181,7 @@ static int get_iovec_page_array(const struct iovec __user *iov, 
		int i;



		error = -EFAULT;

		if (copy_from_user_mmap_sem(&entry, iov, sizeof(entry)))

		if (copy_from_user(&entry, iov, sizeof(entry)))

			break;



		base = entry.iov_base;
@@ -1247,9 +1215,8 @@ static int get_iovec_page_array(const struct iovec __user *iov, 
		if (npages > PIPE_BUFFERS - buffers)

			npages = PIPE_BUFFERS - buffers;



		error = get_user_pages(current, current->mm,

				       (unsigned long) base, npages, 0, 0,

				       &pages[buffers], NULL);

		error = get_user_pages_fast((unsigned long)base, npages,

					0, &pages[buffers]);



		if (unlikely(error <= 0))

			break;
@@ -1288,8 +1255,6 @@ static int get_iovec_page_array(const struct iovec __user *iov, 
		iov++;

	}



	up_read(&current->mm->mmap_sem);



	if (buffers)

		return buffers;