mm/mglru: clean up workingset

mm/mglru: clean up workingset

Patch series "mm/mglru: performance optimizations", v4.

This series improves performance for some previously reported test cases.
Most of the code changes gathered here has been floating on the mailing
list [1][2].  They are now properly organized and have gone through
various benchmarks on client and server devices, including Android, FIO,
memcached, multiple VMs and MongoDB.

In addition to the syzbot regressions fixed in v2 [3] and v3 [4], this
version fixes two more regressions: one reported by Oliver Sang [5] and
the other by Barry Song.

[1] https://lore.kernel.org/CAOUHufahuWcKf5f1Sg3emnqX+cODuR=2TQo7T4Gr-QYLujn4RA@mail.gmail.com/
[2] https://lore.kernel.org/CAOUHufawNerxqLm7L9Yywp3HJFiYVrYO26ePUb1jH-qxNGWzyA@mail.gmail.com/
[3] https://lore.kernel.org/67294349.050a0220.701a.0010.GAE@google.com/
[4] https://lore.kernel.org/67549eca.050a0220.2477f.001b.GAE@google.com/
[5] https://lore.kernel.org/202412231601.f1eb8f84-lkp@intel.com/

This patch (of 7):

Move VM_BUG_ON_FOLIO() to cover both the default and MGLRU paths.  Also
use a pair of rcu_read_lock() and rcu_read_unlock() within each path, to
improve readability.

This change should not have any side effects.

Link: https://lkml.kernel.org/r/20241231043538.4075764-1-yuzhao@google.com
Link: https://lkml.kernel.org/r/20241231043538.4075764-2-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Bharata B Rao <bharata@amd.com>
Cc: David Stevens <stevensd@chromium.org>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>