The quilt patch titled
Subject: mm: remove lock_page_memcg() from rmap
has been removed from the -mm tree. Its filename was
mm-remove-lock_page_memcg-from-rmap.patch
This patch was dropped because it was nacked
------------------------------------------------------
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: remove lock_page_memcg() from rmap
Date: Wed, 23 Nov 2022 13:18:38 -0500
rmap changes (mapping and unmapping) of a page currently take
lock_page_memcg() to serialize 1) update of the mapcount and the cgroup
mapped counter with 2) cgroup moving the page and updating the old cgroup
and the new cgroup counters based on page_mapped().
Before b2052564e66d ("mm: memcontrol: continue cache reclaim from offlined
groups"), we used to reassign all pages that could be found on a cgroup's
LRU list on deletion - something that rmap didn't naturally serialize
against. Since that commit, however, the only pages that get moved are
those mapped into page tables of a task that's being migrated. In that
case, the pte lock is always held (and we know the page is mapped), which
keeps rmap changes at bay already.
The additional lock_page_memcg() by rmap is redundant. Remove it.
Link: https://lkml.kernel.org/r/20221123181838.1373440-1-hannes@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 35 ++++++++++++++++++++---------------
mm/rmap.c | 12 ------------
2 files changed, 20 insertions(+), 27 deletions(-)
--- a/mm/memcontrol.c~mm-remove-lock_page_memcg-from-rmap
+++ a/mm/memcontrol.c
@@ -5676,7 +5676,10 @@ static struct page *mc_handle_file_pte(s
* @from: mem_cgroup which the page is moved from.
* @to: mem_cgroup which the page is moved to. @from != @to.
*
- * The caller must make sure the page is not on LRU (isolate_page() is useful.)
+ * This function acquires folio_lock() and folio_lock_memcg(). The
+ * caller must exclude all other possible ways of accessing
+ * page->memcg, such as LRU isolation (to lock out isolation) and
+ * having the page mapped and pte-locked (to lock out rmap).
*
* This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
* from old cgroup.
@@ -5697,6 +5700,13 @@ static int mem_cgroup_move_account(struc
VM_BUG_ON(compound && !folio_test_large(folio));
/*
+ * We're only moving pages mapped into the moving process's
+ * page tables. The caller's pte lock prevents rmap from
+ * removing the NR_x_MAPPED state while we transfer it.
+ */
+ VM_WARN_ON_ONCE(!folio_mapped(folio));
+
+ /*
* Prevent mem_cgroup_migrate() from looking at
* page's memory cgroup of its source page while we change it.
*/
@@ -5715,30 +5725,25 @@ static int mem_cgroup_move_account(struc
folio_memcg_lock(folio);
if (folio_test_anon(folio)) {
- if (folio_mapped(folio)) {
- __mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
- __mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
- if (folio_test_transhuge(folio)) {
- __mod_lruvec_state(from_vec, NR_ANON_THPS,
- -nr_pages);
- __mod_lruvec_state(to_vec, NR_ANON_THPS,
- nr_pages);
- }
+ __mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
+ __mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
+
+ if (folio_test_transhuge(folio)) {
+ __mod_lruvec_state(from_vec, NR_ANON_THPS, -nr_pages);
+ __mod_lruvec_state(to_vec, NR_ANON_THPS, nr_pages);
}
} else {
__mod_lruvec_state(from_vec, NR_FILE_PAGES, -nr_pages);
__mod_lruvec_state(to_vec, NR_FILE_PAGES, nr_pages);
+ __mod_lruvec_state(from_vec, NR_FILE_MAPPED, -nr_pages);
+ __mod_lruvec_state(to_vec, NR_FILE_MAPPED, nr_pages);
+
if (folio_test_swapbacked(folio)) {
__mod_lruvec_state(from_vec, NR_SHMEM, -nr_pages);
__mod_lruvec_state(to_vec, NR_SHMEM, nr_pages);
}
- if (folio_mapped(folio)) {
- __mod_lruvec_state(from_vec, NR_FILE_MAPPED, -nr_pages);
- __mod_lruvec_state(to_vec, NR_FILE_MAPPED, nr_pages);
- }
-
if (folio_test_dirty(folio)) {
struct address_space *mapping = folio_mapping(folio);
--- a/mm/rmap.c~mm-remove-lock_page_memcg-from-rmap
+++ a/mm/rmap.c
@@ -1222,9 +1222,6 @@ void page_add_anon_rmap(struct page *pag
bool compound = flags & RMAP_COMPOUND;
bool first = true;
- if (unlikely(PageKsm(page)))
- lock_page_memcg(page);
-
/* Is page being mapped by PTE? Is this its first map to be added? */
if (likely(!compound)) {
first = atomic_inc_and_test(&page->_mapcount);
@@ -1254,9 +1251,6 @@ void page_add_anon_rmap(struct page *pag
if (nr)
__mod_lruvec_page_state(page, NR_ANON_MAPPED, nr);
- if (unlikely(PageKsm(page)))
- unlock_page_memcg(page);
-
/* address might be in next vma when migration races vma_adjust */
else if (first)
__page_set_anon_rmap(page, vma, address,
@@ -1321,7 +1315,6 @@ void page_add_file_rmap(struct page *pag
bool first;
VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
- lock_page_memcg(page);
/* Is page being mapped by PTE? Is this its first map to be added? */
if (likely(!compound)) {
@@ -1349,7 +1342,6 @@ void page_add_file_rmap(struct page *pag
NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
if (nr)
__mod_lruvec_page_state(page, NR_FILE_MAPPED, nr);
- unlock_page_memcg(page);
mlock_vma_page(page, vma, compound);
}
@@ -1378,8 +1370,6 @@ void page_remove_rmap(struct page *page,
return;
}
- lock_page_memcg(page);
-
/* Is page being unmapped by PTE? Is this its last map to be removed? */
if (likely(!compound)) {
last = atomic_add_negative(-1, &page->_mapcount);
@@ -1427,8 +1417,6 @@ void page_remove_rmap(struct page *page,
* and remember that it's only reliable while mapped.
*/
- unlock_page_memcg(page);
-
munlock_vma_page(page, vma, compound);
}
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
mm-vmscan-split-khugepaged-stats-from-direct-reclaim-stats.patch
