mm,thp,rmap: handle the normal !PageCompound case first

Commit ("mm,thp,rmap: lock_compound_mapcounts() on THP mapcounts")
propagated the "if (compound) {lock} else if (PageCompound) {lock} else
{atomic}" pattern throughout; but Linus hated the way that gives primacy
to the uncommon case: switch to "if (!PageCompound) {atomic} else if
(compound) {lock} else {lock}" throughout.  Linus has a bigger idea for
how to improve it all, but here just make that rearrangement.

Link: https://lkml.kernel.org/r/fca2f694-2098-b0ef-d4e-f1d8b94d318c@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/rmap.c b/mm/rmap.c
index 512e53c..4833d28 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1311,7 +1311,11 @@ void page_add_anon_rmap(struct page *page,
        else
                VM_BUG_ON_PAGE(!PageLocked(page), page);
 
-       if (compound && PageTransHuge(page)) {
+       if (likely(!PageCompound(page))) {
+               first = atomic_inc_and_test(&page->_mapcount);
+               nr = first;
+
+       } else if (compound && PageTransHuge(page)) {
                lock_compound_mapcounts(page, &mapcounts);
                first = !mapcounts.compound_mapcount;
                mapcounts.compound_mapcount++;
@@ -1321,8 +1325,7 @@ void page_add_anon_rmap(struct page *page,
                                nr = nr_subpages_unmapped(page, nr_pmdmapped);
                }
                unlock_compound_mapcounts(page, &mapcounts);
-
-       } else if (PageCompound(page)) {
+       } else {
                struct page *head = compound_head(page);
 
                lock_compound_mapcounts(head, &mapcounts);
@@ -1330,10 +1333,6 @@ void page_add_anon_rmap(struct page *page,
                first = subpage_mapcount_inc(page);
                nr = first && !mapcounts.compound_mapcount;
                unlock_compound_mapcounts(head, &mapcounts);
-
-       } else {
-               first = atomic_inc_and_test(&page->_mapcount);
-               nr = first;
        }
 
        VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page);
@@ -1373,20 +1372,23 @@ void page_add_anon_rmap(struct page *page,
 void page_add_new_anon_rmap(struct page *page,
        struct vm_area_struct *vma, unsigned long address)
 {
-       const bool compound = PageCompound(page);
-       int nr = compound ? thp_nr_pages(page) : 1;
+       int nr;
 
        VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
        __SetPageSwapBacked(page);
-       if (compound) {
+
+       if (likely(!PageCompound(page))) {
+               /* increment count (starts at -1) */
+               atomic_set(&page->_mapcount, 0);
+               nr = 1;
+       } else {
                VM_BUG_ON_PAGE(!PageTransHuge(page), page);
                /* increment count (starts at -1) */
                atomic_set(compound_mapcount_ptr(page), 0);
+               nr = thp_nr_pages(page);
                __mod_lruvec_page_state(page, NR_ANON_THPS, nr);
-       } else {
-               /* increment count (starts at -1) */
-               atomic_set(&page->_mapcount, 0);
        }
+
        __mod_lruvec_page_state(page, NR_ANON_MAPPED, nr);
        __page_set_anon_rmap(page, vma, address, 1);
 }
@@ -1409,7 +1411,11 @@ void page_add_file_rmap(struct page *page,
        VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
        lock_page_memcg(page);
 
-       if (compound && PageTransHuge(page)) {
+       if (likely(!PageCompound(page))) {
+               first = atomic_inc_and_test(&page->_mapcount);
+               nr = first;
+
+       } else if (compound && PageTransHuge(page)) {
                lock_compound_mapcounts(page, &mapcounts);
                first = !mapcounts.compound_mapcount;
                mapcounts.compound_mapcount++;
@@ -1419,8 +1425,7 @@ void page_add_file_rmap(struct page *page,
                                nr = nr_subpages_unmapped(page, nr_pmdmapped);
                }
                unlock_compound_mapcounts(page, &mapcounts);
-
-       } else if (PageCompound(page)) {
+       } else {
                struct page *head = compound_head(page);
 
                lock_compound_mapcounts(head, &mapcounts);
@@ -1428,10 +1433,6 @@ void page_add_file_rmap(struct page *page,
                first = subpage_mapcount_inc(page);
                nr = first && !mapcounts.compound_mapcount;
                unlock_compound_mapcounts(head, &mapcounts);
-
-       } else {
-               first = atomic_inc_and_test(&page->_mapcount);
-               nr = first;
        }
 
        if (nr_pmdmapped)
@@ -1471,7 +1472,11 @@ void page_remove_rmap(struct page *page,
        lock_page_memcg(page);
 
        /* page still mapped by someone else? */
-       if (compound && PageTransHuge(page)) {
+       if (likely(!PageCompound(page))) {
+               last = atomic_add_negative(-1, &page->_mapcount);
+               nr = last;
+
+       } else if (compound && PageTransHuge(page)) {
                lock_compound_mapcounts(page, &mapcounts);
                mapcounts.compound_mapcount--;
                last = !mapcounts.compound_mapcount;
@@ -1481,8 +1486,7 @@ void page_remove_rmap(struct page *page,
                                nr = nr_subpages_unmapped(page, nr_pmdmapped);
                }
                unlock_compound_mapcounts(page, &mapcounts);
-
-       } else if (PageCompound(page)) {
+       } else {
                struct page *head = compound_head(page);
 
                lock_compound_mapcounts(head, &mapcounts);
@@ -1490,10 +1494,6 @@ void page_remove_rmap(struct page *page,
                last = subpage_mapcount_dec(page);
                nr = last && !mapcounts.compound_mapcount;
                unlock_compound_mapcounts(head, &mapcounts);
-
-       } else {
-               last = atomic_add_negative(-1, &page->_mapcount);
-               nr = last;
        }
 
        if (nr_pmdmapped) {