Commit bb7f5d96 authored by Andreas Gruenbacher's avatar Andreas Gruenbacher
Browse files

gfs2: Fix should_fault_in_pages() logic 



Fix the fault-in window size logic:
* Use a maximum window size of 1 MiB instead of BIO_MAX_VECS * PAGE_SIZE.
  The previous window size was always one page because the pages variable
  was accidentally being defined and then redefined in
  should_fault_in_pages().
* The nr_dirtied heuristic for guessing when there might be memory
  pressure often results in very small window sizes.  Don't let
  nr_dirtied drop below 8 pages (as btrfs does).
* Compute the window size in units of bytes, not pages.
* Account for page overlap (unaligned iterators).

Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
parent b2963932

fs/gfs2/file.c

+9 −8
Original line number Diff line number Diff line
@@ -775,8 +775,7 @@ static inline bool should_fault_in_pages(ssize_t ret, struct iov_iter *i, 
					 size_t *window_size)

{

	size_t count = iov_iter_count(i);

	char __user *p;

	int pages = 1;

	size_t size, offs;



	if (likely(!count))

		return false;
@@ -785,18 +784,20 @@ static inline bool should_fault_in_pages(ssize_t ret, struct iov_iter *i, 
	if (!iter_is_iovec(i))

		return false;



	size = PAGE_SIZE;

	offs = offset_in_page(i->iov[0].iov_base + i->iov_offset);

	if (*prev_count != count || !*window_size) {

		int pages, nr_dirtied;

		size_t nr_dirtied;



		pages = min_t(int, BIO_MAX_VECS, DIV_ROUND_UP(count, PAGE_SIZE));

		size = ALIGN(offs + count, PAGE_SIZE);

		size = min_t(size_t, size, SZ_1M);

		nr_dirtied = max(current->nr_dirtied_pause -

				 current->nr_dirtied, 1);

		pages = min(pages, nr_dirtied);

				 current->nr_dirtied, 8);

		size = min(size, nr_dirtied << PAGE_SHIFT);

	}



	*prev_count = count;

	p = i->iov[0].iov_base + i->iov_offset;

	*window_size = (size_t)PAGE_SIZE * pages - offset_in_page(p);

	*window_size = size - offs;

	return true;

}