mm: inline simpler case of page_remove_file_rmap()

Now that we have a simplified special case of 'page_remove_rmap()' that
doesn't deal with the 'compound' case and always gets a file-mapped (ie
not anonymous) page, it ended up doing just

	lock_page_memcg(page);
	page_remove_file_rmap(page, false);
	unlock_page_memcg(page);

but 'page_remove_file_rmap()' is actually trivial when 'compound' is false.

So just inline that non-compound case in the caller, and - like we did
in the previous commit for the anon pages - only do the memcg locking for
the parts that actually matter: the page statistics.

Also, as the previous commit did for anonymous pages, knowing we only
get called for the last-level page table entries allows for a further
simplification: we can get rid of the 'PageHuge(page)' case too.

You can't map a huge-page in a pte without splitting it (and the full
code in the generic page_remove_file_rmap() function has a comment to
that effect: "hugetlb pages are always mapped with pmds").

That means that the page_zap_file_rmap() case of that whole function is
really small and trivial.

Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 71a5365f23f3..69de6c833d5c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1426,8 +1426,11 @@ static void page_remove_anon_compound_rmap(struct page *page)
  */
 void page_zap_file_rmap(struct page *page)
 {
+	if (!atomic_add_negative(-1, &page->_mapcount))
+		return;
+
 	lock_page_memcg(page);
-	page_remove_file_rmap(page, false);
+	__dec_lruvec_page_state(page, NR_FILE_MAPPED);
 	unlock_page_memcg(page);
 }