Re: [PATCH rfc 0/3] mm: allow more high-order pages stored on PCP lists

[Barry Song <21cnbao@gmail.com>]

On Mon, Apr 15, 2024 at 8:12 PM Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
>
> Both the file pages and anonymous pages support large folio, high-order
> pages except PMD_ORDER will also be allocated frequently which could
> increase the zone lock contention, allow high-order pages on pcp lists
> could reduce the big zone lock contention, but as commit 44042b449872
> ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> pointed, it may not win in all the scenes, add a new control sysfs to
> enable or disable specified high-order pages stored on PCP lists, the order
> (PAGE_ALLOC_COSTLY_ORDER, PMD_ORDER) won't be stored on PCP list by default.

This is precisely something Baolin and I have discussed and intended
to implement[1],
but unfortunately, we haven't had the time to do so.

[1] https://lore.kernel.org/linux-mm/13c59ca8-baac-405e-8640-e693c78ef79a@suse.cz/T/#mecb0514ced830ac4df320113bedd7073bea9ab7a

>
> With perf lock tools, the lock contention from will-it-scale page_fault1
> (with 90 tasks run 10s, hugepage-2048KB never, hugepage-64K always) show
> below(only care about zone spinlock and pcp spinlock),
>
> Without patches,
>  contended   total wait     max wait     avg wait         type   caller
>        713      4.64 ms     74.37 us      6.51 us     spinlock   __alloc_pages+0x23c
>
> With patches,
>  contended   total wait     max wait     avg wait         type   caller
>          2     25.66 us     16.31 us     12.83 us     spinlock   rmqueue_pcplist+0x2b0
>
> Similar results on shell8 from unixbench,
>
> Without patches,
>       4942    901.09 ms      1.31 ms    182.33 us     spinlock   __alloc_pages+0x23c
>       1556    298.76 ms      1.23 ms    192.01 us     spinlock   rmqueue_pcplist+0x2b0
>        991    182.73 ms    879.80 us    184.39 us     spinlock   rmqueue_pcplist+0x2b0
>
> With patches,
> contended   total wait     max wait     avg wait         type   caller
>        988    187.63 ms    855.18 us    189.91 us     spinlock   rmqueue_pcplist+0x2b0
>        505     88.99 ms    793.27 us    176.21 us     spinlock   rmqueue_pcplist+0x2b0
>
> The Benchmarks Score shows a little improvoment(0.28%) from shell8, but the
> zone lock from __alloc_pages() disappeared.
>
> Kefeng Wang (3):
>   mm: prepare more high-order pages to be stored on the per-cpu lists
>   mm: add control to allow specified high-order pages stored on PCP list
>   mm: pcp: show each order page count
>
>  Documentation/admin-guide/mm/transhuge.rst | 11 ++++
>  include/linux/gfp.h                        |  1 +
>  include/linux/huge_mm.h                    |  1 +
>  include/linux/mmzone.h                     | 10 ++-
>  include/linux/vmstat.h                     | 19 ++++++
>  mm/Kconfig.debug                           |  8 +++
>  mm/huge_memory.c                           | 74 ++++++++++++++++++++++
>  mm/page_alloc.c                            | 30 +++++++--
>  mm/vmstat.c                                | 16 +++++
>  9 files changed, 164 insertions(+), 6 deletions(-)
>
> --
> 2.27.0
>
>