mm/mglru: optimize deactivation

Do not shuffle a folio in the deactivation paths if it is already in the
oldest generation.  This reduces the LRU lock contention.

Before this patch, the contention is reproducible by FIO, e.g.,

  fio -filename=/dev/nvme1n1p2 -direct=0 -thread -size=1024G \
      -rwmixwrite=30  --norandommap --randrepeat=0 -ioengine=sync \
      -bs=4k -numjobs=400 -runtime=25000 --time_based \
      -group_reporting -name=mglru

  98.96%--_raw_spin_lock_irqsave
          folio_lruvec_lock_irqsave
          |
           --98.78%--folio_batch_move_lru
               |
                --98.63%--deactivate_file_folio
                          mapping_try_invalidate
                          invalidate_mapping_pages
                          invalidate_bdev
                          blkdev_common_ioctl
                          blkdev_ioctl

After this patch, deactivate_file_folio() bails out early without taking
the LRU lock.

A side effect is that a folio can be left at the head of the oldest
generation, rather than the tail.  If reclaim happens at the same time, it
cannot reclaim this folio immediately.  Since there is no known
correlation between truncation and reclaim, this side effect is considered
insignificant.

Link: https://lkml.kernel.org/r/20241231043538.4075764-3-yuzhao@google.com


Reported-by: Bharata B Rao <bharata@amd.com>
Closes: https://lore.kernel.org/CAOUHufawNerxqLm7L9Yywp3HJFiYVrYO26ePUb1jH-qxNGWzyA@mail.gmail.com/


Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: David Stevens <stevensd@chromium.org>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>