gfs2: Align read and write chunks to the page cache

Align the chunks that reads and writes are carried out in to the page
cache rather than the user buffers.  This will be more efficient in
general, especially for allocating writes.  Optimizing the case that the
user buffer is gfs2 backed isn't very useful; we only need to make sure
we won't deadlock.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/file.c

@@ -771,6 +771,7 @@ static int gfs2_fsync(struct file *file, loff_t start, loff_t end,
 }
 
 static inline bool should_fault_in_pages(struct iov_iter *i,
+					 struct kiocb *iocb,
 					 size_t *prev_count,
 					 size_t *window_size)
 {
@@ -783,15 +784,13 @@ static inline bool should_fault_in_pages(struct iov_iter *i,
 		return false;
 
 	size = PAGE_SIZE;
-	offs = offset_in_page(i->iov[0].iov_base + i->iov_offset);
+	offs = offset_in_page(iocb->ki_pos);
 	if (*prev_count != count || !*window_size) {
 		size_t nr_dirtied;
 
-		size = ALIGN(offs + count, PAGE_SIZE);
-		size = min_t(size_t, size, SZ_1M);
 		nr_dirtied = max(current->nr_dirtied_pause -
 				 current->nr_dirtied, 8);
-		size = min(size, nr_dirtied << PAGE_SHIFT);
+		size = min_t(size_t, SZ_1M, nr_dirtied << PAGE_SHIFT);
 	}
 
 	*prev_count = count;
@@ -845,7 +844,7 @@ static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to,
 	if (ret > 0)
 		read = ret;
 
-	if (should_fault_in_pages(to, &prev_count, &window_size)) {
+	if (should_fault_in_pages(to, iocb, &prev_count, &window_size)) {
 		gfs2_holder_allow_demote(gh);
 		window_size -= fault_in_iov_iter_writeable(to, window_size);
 		gfs2_holder_disallow_demote(gh);
@@ -916,7 +915,7 @@ static ssize_t gfs2_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
 	if (ret > 0)
 		written = ret;
 
-	if (should_fault_in_pages(from, &prev_count, &window_size)) {
+	if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
 		gfs2_holder_allow_demote(gh);
 		window_size -= fault_in_iov_iter_readable(from, window_size);
 		gfs2_holder_disallow_demote(gh);
@@ -984,7 +983,7 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	if (ret > 0)
 		read += ret;
 
-	if (should_fault_in_pages(to, &prev_count, &window_size)) {
+	if (should_fault_in_pages(to, iocb, &prev_count, &window_size)) {
 		gfs2_holder_allow_demote(&gh);
 		window_size -= fault_in_iov_iter_writeable(to, window_size);
 		gfs2_holder_disallow_demote(&gh);
@@ -1061,7 +1060,7 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb,
 		goto out_unlock;
 
 	from->count = orig_count - written;
-	if (should_fault_in_pages(from, &prev_count, &window_size)) {
+	if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
 		gfs2_holder_allow_demote(gh);
 		window_size -= fault_in_iov_iter_readable(from, window_size);
 		gfs2_holder_disallow_demote(gh);