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Date: Thu, 1 Feb 2018 23:18:01 -0500
From: Daniel Jordan <daniel.m.jordan@...cle.com>
To: Steven Whitehouse <swhiteho@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: aaron.lu@...el.com, ak@...ux.intel.com, akpm@...ux-foundation.org,
Dave.Dice@...cle.com, dave@...olabs.net,
khandual@...ux.vnet.ibm.com, ldufour@...ux.vnet.ibm.com,
mgorman@...e.de, mhocko@...nel.org, pasha.tatashin@...cle.com,
steven.sistare@...cle.com, yossi.lev@...cle.com
Subject: Re: [RFC PATCH v1 00/13] lru_lock scalability
On 02/01/2018 10:54 AM, Steven Whitehouse wrote:
> Hi,
>
>
> On 31/01/18 23:04, daniel.m.jordan@...cle.com wrote:
>> 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.
> GFS2 has an lru list for glocks, which can be contended under certain workloads. Work is still ongoing to figure out exactly why, but this looks like it might be a good approach to that issue too. The main purpose of GFS2's lru list is to allow shrinking of the glocks under memory pressure via the gfs2_scan_glock_lru() function, and it looks like this type of approach could be used there to improve the scalability,
Glad to hear that this could help in gfs2 as well.
Hopefully struct gfs2_glock is less space constrained than struct page for storing the few bits of metadata that this approach requires.
Daniel
>
> Steve.
>
>>
>> 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(-)
>>
>
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