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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





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@xxxxxxxxxx> 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@xxxxxxxxxx> 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").






[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux