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List:       linux-kernel
Subject:    [RFC PATCH v1 00/13] lru_lock scalability
From:       daniel.m.jordan () oracle ! com
Date:       2018-01-31 23:04:00
Message-ID: 20180131230413.27653-1-daniel.m.jordan () oracle ! com
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lru_lock, a per-node* spinlock that protects an LRU list, is one of the
hottest locks in the kernel.  On some workloads on large machines, it
shows up at the top of lock_stat.

One way to improve lru_lock scalability is to introduce an array of locks,
with each lock protecting certain batches of LRU pages.

        *ooooooooooo**ooooooooooo**ooooooooooo**oooo ...
        |           ||           ||           ||
         \ batch 1 /  \ batch 2 /  \ batch 3 /  

In this ASCII depiction of an LRU, a page is represented with either '*'
or 'o'.  An asterisk indicates a sentinel page, which is a page at the
edge of a batch.  An 'o' indicates a non-sentinel page.

To remove a non-sentinel LRU page, only one lock from the array is
required.  This allows multiple threads to remove pages from different
batches simultaneously.  A sentinel page requires lru_lock in addition to
a lock from the array.

Full performance numbers appear in the last patch in this series, but this
prototype allows a microbenchmark to do up to 28% more page faults per
second with 16 or more concurrent processes.

This work was developed in collaboration with Steve Sistare.

Note: This is an early prototype.  I'm submitting it now to support my
request to attend LSF/MM, as well as get early feedback on the idea.  Any
comments appreciated.


* lru_lock is actually per-memcg, but without memcg's in the picture it
  becomes per-node.


Aaron Lu (1):
  mm: add a percpu_pagelist_batch sysctl interface

Daniel Jordan (12):
  mm: allow compaction to be disabled
  mm: add lock array to pgdat and batch fields to struct page
  mm: introduce struct lru_list_head in lruvec to hold per-LRU batch
    info
  mm: add batching logic to add/delete/move API's
  mm: add lru_[un]lock_all APIs
  mm: convert to-be-refactored lru_lock callsites to lock-all API
  mm: temporarily convert lru_lock callsites to lock-all API
  mm: introduce add-only version of pagevec_lru_move_fn
  mm: add LRU batch lock API's
  mm: use lru_batch locking in release_pages
  mm: split up release_pages into non-sentinel and sentinel passes
  mm: splice local lists onto the front of the LRU

 include/linux/mm_inline.h | 209 +++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/mm_types.h  |   5 ++
 include/linux/mmzone.h    |  25 +++++-
 kernel/sysctl.c           |   9 ++
 mm/Kconfig                |   1 -
 mm/huge_memory.c          |   6 +-
 mm/memcontrol.c           |   5 +-
 mm/mlock.c                |  11 +--
 mm/mmzone.c               |   7 +-
 mm/page_alloc.c           |  43 +++++++++-
 mm/page_idle.c            |   4 +-
 mm/swap.c                 | 208 ++++++++++++++++++++++++++++++++++++---------
 mm/vmscan.c               |  49 +++++------
 13 files changed, 500 insertions(+), 82 deletions(-)

-- 
2.16.1

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