The patch titled
Subject: mm,thp,rmap: handle the normal !PageCompound case first
has been added to the -mm mm-unstable branch. Its filename is
mmthprmap-handle-the-normal-pagecompound-case-first.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmthprmap-handle-the-normal-pagecompound-case-first.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm,thp,rmap: handle the normal !PageCompound case first
Date: Wed, 9 Nov 2022 18:18:49 -0800 (PST)
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@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mina Almasry <almasrymina@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 54 ++++++++++++++++++++++++++--------------------------
1 file changed, 27 insertions(+), 27 deletions(-)
--- a/mm/rmap.c~mmthprmap-handle-the-normal-pagecompound-case-first
+++ a/mm/rmap.c
@@ -1311,7 +1311,11 @@ void page_add_anon_rmap(struct page *pag
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 *pag
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 *pag
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 *pag
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 *pag
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 *pag
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 *pag
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) {
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mmhugetlb-use-folio-fields-in-second-tail-page.patch
mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch
mmthprmap-simplify-compound-page-mapcount-handling.patch
mmthprmap-lock_compound_mapcounts-on-thp-mapcounts.patch
mmthprmap-handle-the-normal-pagecompound-case-first.patch
