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SubjectRe: [RFC PATCH v1 00/13] lru_lock scalability
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Hi,


On 31/01/18 23:04, daniel.m.jordan@oracle.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,

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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