[PATCH v20 00/20] per memcg lru lock

Alex Shi
2020-10-29T10:45:38Z

This version just a rebase on v5.10-rc1. and moves the lru_lock position
down after lists[] in lruvec, which resolves a fio.read regression that
revealed by Rong Chen -- Intel LKP.

Many thanks for line by line review by Hugh Dickins and Alexander Duyck.

So now this patchset includes 3 parts:
1, some code cleanup and minimum optimization as a preparation.
2, use TestCleanPageLRU as page isolation's precondition.
3, replace per node lru_lock with per memcg per node lru_lock.

Current lru_lock is one for each of node, pgdat->lru_lock, that guard for
lru lists, but now we had moved the lru lists into memcg for long time. Still
using per node lru_lock is clearly unscalable, pages on each of memcgs have
to compete each others for a whole lru_lock. This patchset try to use per
lruvec/memcg lru_lock to repleace per node lru lock to guard lru lists, make
it scalable for memcgs and get performance gain.

Currently lru_lock still guards both lru list and page's lru bit, that's ok.
but if we want to use specific lruvec lock on the page, we need to pin down
the page's lruvec/memcg during locking. Just taking lruvec lock first may be
undermined by the page's memcg charge/migration. To fix this problem, we could
take out the page's lru bit clear and use it as pin down action to block the
memcg changes. That's the reason for new atomic func TestClearPageLRU.
So now isolating a page need both actions: TestClearPageLRU and hold the
lru_lock.

The typical usage of this is isolate_migratepages_block() in compaction.c
we have to take lru bit before lru lock, that serialized the page isolation
in memcg page charge/migration which will change page's lruvec and new
lru_lock in it.

The above solution suggested by Johannes Weiner, and based on his new memcg
charge path, then have this patchset. (Hugh Dickins tested and contributed much
code from compaction fix to general code polish, thanks a lot!).

Daniel Jordan's testing show 62% improvement on modified readtwice case
on his 2P * 10 core * 2 HT broadwell box on v18, which has no much different
with this v20.
https://lore.kernel.org/lkml/20200915165807.kpp7uhiw7l3loofu@ca-dmjordan1.us.oracle.com/

Thanks Hugh Dickins and Konstantin Khlebnikov, they both brought this
idea 8 years ago, and others who give comments as well: Daniel Jordan,
Mel Gorman, Shakeel Butt, Matthew Wilcox, Alexander Duyck etc.

Thanks for Testing support from Intel 0day and Rong Chen, Fengguang Wu,
and Yun Wang. Hugh Dickins also shared his kbuild-swap case. Thanks!

Alex Shi (17):
mm/memcg: warning on !memcg after readahead page charged
mm/memcg: bail early from swap accounting if memcg disabled
mm/thp: move lru_add_page_tail func to huge_memory.c
mm/thp: use head for head page in lru_add_page_tail
mm/thp: Simplify lru_add_page_tail()
mm/thp: narrow lru locking
mm/vmscan: remove unnecessary lruvec adding
mm/memcg: add debug checking in lock_page_memcg
mm/swap.c: fold vm event PGROTATED into pagevec_move_tail_fn
mm/lru: move lock into lru_note_cost
mm/vmscan: remove lruvec reget in move_pages_to_lru
mm/mlock: remove lru_lock on TestClearPageMlocked
mm/mlock: remove __munlock_isolate_lru_page
mm/lru: introduce TestClearPageLRU
mm/compaction: do page isolation first in compaction
mm/swap.c: serialize memcg changes in pagevec_lru_move_fn
mm/lru: replace pgdat lru_lock with lruvec lock

Alexander Duyck (1):
mm/lru: introduce the relock_page_lruvec function

Hugh Dickins (2):
mm: page_idle_get_page() does not need lru_lock
mm/lru: revise the comments of lru_lock

Documentation/admin-guide/cgroup-v1/memcg_test.rst | 15 +-
Documentation/admin-guide/cgroup-v1/memory.rst | 21 +--
Documentation/trace/events-kmem.rst | 2 +-
Documentation/vm/unevictable-lru.rst | 22 +--
include/linux/memcontrol.h | 110 +++++++++++
include/linux/mm_types.h | 2 +-
include/linux/mmdebug.h | 13 ++
include/linux/mmzone.h | 6 +-
include/linux/page-flags.h | 1 +
include/linux/swap.h | 4 +-
mm/compaction.c | 94 +++++++---
mm/filemap.c | 4 +-
mm/huge_memory.c | 45 +++--
mm/memcontrol.c | 85 ++++++++-
mm/mlock.c | 63 ++-----
mm/mmzone.c | 1 +
mm/page_alloc.c | 1 -
mm/page_idle.c | 4 -
mm/rmap.c | 4 +-
mm/swap.c | 199 ++++++++------------
mm/vmscan.c | 203 +++++++++++----------
mm/workingset.c | 2 -
22 files changed, 523 insertions(+), 378 deletions(-)

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1.8.3.1