Revert "mm: align larger anonymous mappings on THP boundaries"

This reverts commit f35b5d7.

It has been reported to cause huge performance regressions on some loads
(will-it-scale.per_process_ops, but also building the kernel with
clang).

The commit did speed up gcc builds by a small amount, so it's not an
unambiguous regression, but until the big regressions are understood,
let's revert it.

Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reported-by: Nathan Chancellor <[email protected]>
Link: https://lore.kernel.org/lkml/Y1DNQaoPWxE%[email protected]/
Cc: Huang, Ying <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Yang Shi <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: torvalds

mm/mmap.c

@@ -1779,9 +1779,6 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 		 */
 		pgoff = 0;
 		get_area = shmem_get_unmapped_area;
-	} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
-		/* Ensures that larger anonymous mappings are THP aligned. */
-		get_area = thp_get_unmapped_area;
 	}
 
 	addr = get_area(file, addr, len, pgoff, flags);