linux-kernel - [PATCH 0/7] revert shrinker

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Message-Id: <20230609081518.3039120-1-qi.zheng@linux.dev>
Date:   Fri,  9 Jun 2023 08:15:11 +0000
From:   Qi Zheng <qi.zheng@...ux.dev>
To:     akpm@...ux-foundation.org
Cc:     david@...morbit.com, tkhai@...ru, roman.gushchin@...ux.dev,
        vbabka@...e.cz, muchun.song@...ux.dev, yujie.liu@...el.com,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH 0/7] revert shrinker_srcu related changes

From: Qi Zheng <zhengqi.arch@...edance.com>

Hi all,

Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec
test case [1], which is caused by commit f95bdb700bc6 ("mm: vmscan: make
global slab shrink lockless"). The root cause is that SRCU has to be careful
to not frequently check for SRCU read-side critical section exits. Therefore,
even if no one is currently in the SRCU read-side critical section,
synchronize_srcu() cannot return quickly. That's why unregister_shrinker()
has become slower.

After discussion, we will try to use the refcount+RCU method [2] proposed
by Dave Chinner to continue to re-implement the lockless slab shrink. So
revert the shrinker_srcu related changes first.

[1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/
[2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/

And hi Andrew, the commit c3b5cb881de6 ("mm: vmscan: move
shrinker_debugfs_remove() before synchronize_srcu()") is still in the
mm-unstable branch, you can drop it directly.

This series is based on v6.4-rc5.

Thanks,
Qi

Qi Zheng (7):
  Revert "mm: shrinkers: convert shrinker_rwsem to mutex"
  Revert "mm: vmscan: remove shrinker_rwsem from
    synchronize_shrinkers()"
  Revert "mm: vmscan: hold write lock to reparent shrinker nr_deferred"
  Revert "mm: shrinkers: make count and scan in shrinker debugfs
    lockless"
  Revert "mm: vmscan: add shrinker_srcu_generation"
  Revert "mm: vmscan: make memcg slab shrink lockless"
  Revert "mm: vmscan: make global slab shrink lockless"

 drivers/md/dm-cache-metadata.c |   2 +-
 drivers/md/dm-thin-metadata.c  |   2 +-
 fs/super.c                     |   2 +-
 mm/shrinker_debug.c            |  39 ++++++----
 mm/vmscan.c                    | 125 +++++++++++++++------------------
 5 files changed, 82 insertions(+), 88 deletions(-)

-- 
2.30.2