mm/memory-failure: do pgoff calculation before for_each_process()

There is no need to calculate pgoff in each loop of for_each_process(), so
move it to the place before for_each_process(), which can save some CPU
cycles.
Signed-off-by: NXianting Tian <tian.xianting@h3c.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NNaoya Horiguchi <naoya.horiguchi@nec.com>
Link: http://lkml.kernel.org/r/20200818082647.34322-1-tian.xianting@h3c.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -484,11 +484,12 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
 	struct vm_area_struct *vma;
 	struct task_struct *tsk;
 	struct address_space *mapping = page->mapping;
+	pgoff_t pgoff;
 
 	i_mmap_lock_read(mapping);
 	read_lock(&tasklist_lock);
+	pgoff = page_to_pgoff(page);
 	for_each_process(tsk) {
-		pgoff_t pgoff = page_to_pgoff(page);
 		struct task_struct *t = task_early_kill(tsk, force_early);
 
 		if (!t)