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

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

On 2024/4/16 12:50, Kefeng Wang wrote:
> 
> 
> On 2024/4/16 8:21, Barry Song wrote:
>> On Tue, Apr 16, 2024 at 12:18 AM Kefeng Wang 
>> <wangkefeng.wang@huawei.com> wrote:
>>>
>>>
>>>
>>> On 2024/4/15 18:52, David Hildenbrand wrote:
>>>> On 15.04.24 10:59, Kefeng Wang wrote:
>>>>>
>>>>>
>>>>> 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.
>>>>
>>>> I'm wondering, though, if this is really a suitable candidate for a
>>>> sysctl toggle. Can anybody really come up with an educated guess for
>>>> these values?
>>>
>>> Not sure this is suitable in sysctl, but mTHP anon is enabled in sysctl,
>>> we could trace __alloc_pages() and do order statistic to decide to
>>> choose the high-order to be enabled on PCP.
>>>
>>>>
>>>> Especially reading "Benchmarks Score shows a little improvoment(0.28%)"
>>>> and "it may not win in all the scenes", to me it mostly sounds like
>>>> "minimal impact" -- so who cares?
>>>
>>> Even though lock conflicts are eliminated, there is very limited
>>> performance improvement(even maybe fluctuation), it is not a good
>>> testcase to show improvement, just show the zone-lock issue, we need to
>>> find other better testcase, maybe some test on Andriod(heavy use 64K, no
>>> PMD THP), or LKP maybe give some help?
>>>
>>> I will try to find other testcase to show the benefit.
>>
>> Hi Kefeng,
>>
>> I wonder if you will see some major improvements on mTHP 64KiB using
>> the below microbench I wrote just now, for example perf and time to
>> finish the program
>>
>> #define DATA_SIZE (2UL * 1024 * 1024)
>>
>> int main(int argc, char **argv)
>> {
>>          /* make 32 concurrent alloc and free of mTHP */
>>          fork(); fork(); fork(); fork(); fork();
>>
>>          for (int i = 0; i < 100000; i++) {
>>                  void *addr = mmap(NULL, DATA_SIZE, PROT_READ | 
>> PROT_WRITE,
>>                                  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>>                  if (addr == MAP_FAILED) {
>>                          perror("fail to malloc");
>>                          return -1;
>>                  }
>>                  memset(addr, 0x11, DATA_SIZE);
>>                  munmap(addr, DATA_SIZE);
>>          }
>>
>>          return 0;
>> }
>>

Rebased on next-20240415,

echo never > /sys/kernel/mm/transparent_hugepage/enabled
echo always > /sys/kernel/mm/transparent_hugepage/hugepages-64kB/enabled

Compare with
   echo 0 > /sys/kernel/mm/transparent_hugepage/hugepages-64kB/pcp_enabled
   echo 1 > /sys/kernel/mm/transparent_hugepage/hugepages-64kB/pcp_enabled

> 
> 1) PCP disabled
>      1    2    3    4    5    average
> real    200.41    202.18    203.16    201.54    200.91    201.64
> user    6.49    6.21    6.25    6.31    6.35    6.322
> sys     193.3    195.39    196.3    194.65    194.01    194.73
> 
> 2) PCP enabled
> real    198.25    199.26    195.51    199.28    189.12    196.284       
> -2.66%
> user    6.21    6.02    6.02    6.28    6.21    6.148       -2.75%
> sys     191.46    192.64    188.96    192.47    182.39    189.584       
> -2.64%
> 
> for above test, time reduce 2.x%
> 
> 
> And re-test page_fault1(anon) from will-it-scale
> 
> 1) PCP enabled
> tasks    processes    processes_idle    threads    threads_idle    linear
> 0    0    100    0    100    0
> 1    1416915    98.95    1418128    98.95    1418128
> 20    5327312    79.22    3821312    94.36    28362560
> 40    9437184    58.58    4463657    94.55    56725120
> 60    8120003    38.16    4736716    94.61    85087680
> 80    7356508    18.29    4847824    94.46    113450240
> 100    7256185    1.48    4870096    94.61    141812800
> 
> 2) PCP disabled
> tasks    processes    processes_idle    threads    threads_idle    linear
> 0    0    100    0    100    0
> 1    1365398    98.95    1354502    98.95    1365398
> 20    5174918    79.22    3722368    94.65    27307960
> 40    9094265    58.58    4427267    94.82    54615920
> 60    8021606    38.18    4572896    94.93    81923880
> 80    7497318    18.2    4637062    94.76    109231840
> 100    6819897    1.47    4654521    94.63    136539800
> 
> ------------------------------------
> 1) vs 2)  pcp enabled improve 3.86%
> 
> 3) PCP re-enabled
> tasks    processes    processes_idle    threads    threads_idle    linear
> 0    0    100    0    100    0
> 1    1419036    98.96    1428403    98.95    1428403
> 20    5356092    79.23    3851849    94.41    28568060
> 40    9437184    58.58    4512918    94.63    57136120
> 60    8252342    38.16    4659552    94.68    85704180
> 80    7414899    18.26    4790576    94.77    114272240
> 100    7062902    1.46    4759030    94.64    142840300
> 
> 4) PCP re-disabled
> tasks    processes    processes_idle    threads    threads_idle    linear
> 0    0    100    0    100    0
> 1    1352649    98.95    1354806    98.95    1354806
> 20    5172924    79.22    3719292    94.64    27096120
> 40    9174505    58.59    4310649    94.93    54192240
> 60    8021606    38.17    4552960    94.81    81288360
> 80    7497318    18.18    4671638    94.81    108384480
> 100    6823926    1.47    4725955    94.64    135480600
> 
> ------------------------------------
> 3) vs 4)  pcp enabled improve 5.43%
> 
> Average: 4.645%
> 
> 
> 
> 
> 
>>>
>>>>
>>>> How much is the cost vs. benefit of just having one sane system
>>>> configuration?
>>>>
>>>
>>> For arm64 with 4k, five more high-orders(4~8), five more pcplists,
>>> and for high-orders, we assumes most of them are moveable, but maybe
>>> not, so enable it by default maybe more fragmentization, see
>>> 5d0a661d808f ("mm/page_alloc: use only one PCP list for THP-sized
>>> allocations").
>>>
>