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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/4/15 16:18, Barry Song wrote:
> 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.

Indeed, same thing. Recently, we are working on unixbench/lmbench
optimization, I tested Multi-size THP for anonymous memory by hard-cord
PAGE_ALLOC_COSTLY_ORDER from 3 to 4[1], it shows some improvement but
not for all cases and not very stable, so re-implemented it by according
to the user requirement and enable it dynamically.

[1] 
https://lore.kernel.org/linux-mm/b8f5a47a-af1e-44ed-a89b-460d0be56d2c@huawei.com/

> 
> [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
>>
>>
>