On Wed, Mar 9, 2016 at 12:28 PM, Balbir Singh <bsingharora@xxxxxxxxx> wrote:
>
>
> On 09/03/16 15:17, Li Zhang wrote:
>> On Tue, Mar 8, 2016 at 10:45 PM, Balbir Singh <bsingharora@xxxxxxxxx> wrote:
>>>
>>> On 08/03/16 14:55, Li Zhang wrote:
>>>> From: Li Zhang <zhlcindy@xxxxxxxxxxxxxxxxxx>
>>>>
>>>> Uptream has supported page parallel initialisation for X86 and the
>>>> boot time is improved greately. Some tests have been done for Power.
>>>>
>>>> Here is the result I have done with different memory size.
>>>>
>>>> * 4GB memory:
>>>> boot time is as the following:
>>>> with patch vs without patch: 10.4s vs 24.5s
>>>> boot time is improved 57%
>>>> * 200GB memory:
>>>> boot time looks the same with and without patches.
>>>> boot time is about 38s
>>>> * 32TB memory:
>>>> boot time looks the same with and without patches
>>>> boot time is about 160s.
>>>> The boot time is much shorter than X86 with 24TB memory.
>>>> From community discussion, it costs about 694s for X86 24T system.
>>>>
>>>> From code view, parallel initialisation improve the performance by
>>>> deferring memory initilisation to kswap with N kthreads, it should
>>>> improve the performance therotically.
>>>>
>>>> From the test result, On X86, performance is improved greatly with huge
>>>> memory. But on Power platform, it is improved greatly with less than
>>>> 100GB memory. For huge memory, it is not improved greatly. But it saves
>>>> the time with several threads at least, as the following information
>>>> shows(32TB system log):
>>>>
>>>> [ 22.648169] node 9 initialised, 16607461 pages in 280ms
>>>> [ 22.783772] node 3 initialised, 23937243 pages in 410ms
>>>> [ 22.858877] node 6 initialised, 29179347 pages in 490ms
>>>> [ 22.863252] node 2 initialised, 29179347 pages in 490ms
>>>> [ 22.907545] node 0 initialised, 32049614 pages in 540ms
>>>> [ 22.920891] node 15 initialised, 32212280 pages in 550ms
>>>> [ 22.923236] node 4 initialised, 32306127 pages in 550ms
>>>> [ 22.923384] node 12 initialised, 32314319 pages in 550ms
>>>> [ 22.924754] node 8 initialised, 32314319 pages in 550ms
>>>> [ 22.940780] node 13 initialised, 33353677 pages in 570ms
>>>> [ 22.940796] node 11 initialised, 33353677 pages in 570ms
>>>> [ 22.941700] node 5 initialised, 33353677 pages in 570ms
>>>> [ 22.941721] node 10 initialised, 33353677 pages in 570ms
>>>> [ 22.941876] node 7 initialised, 33353677 pages in 570ms
>>>> [ 22.944946] node 14 initialised, 33353677 pages in 570ms
>>>> [ 22.946063] node 1 initialised, 33345485 pages in 580ms
>>>>
>>>> It saves the time about 550*16 ms at least, although it can be ignore to compare
>>>> the boot time about 160 seconds. What's more, the boot time is much shorter
>>>> on Power even without patches than x86 for huge memory machine.
>>>>
>>>> So this patchset is still necessary to be enabled for Power.
>>>>
>>>>
>> Hi Balbir,
>>
>> Thanks for your reviewing.
>>
>>> The patchset looks good, two questions
>>>
>>> 1. The patchset is still necessary for
>>> a. systems with smaller amount of RAM?
>> I think it is. Currently, I tested systems for 4GB, 50GB, and
>> boot time is improved.
>> We may test more systems with different memory size in the future.
>>> b. Theoretically it improves boot time?
>> The boot time is improved a little bit for huge memory system
>> and it can be ignored.
>> But I think it's still necessary to enable this feature.
>>
>>> 2. the pgdat->node_spanned_pages >> 8 sounds arbitrary
>>> On a system with 2TB*16 nodes, it would initialize about 8GB before calling deferred init?
>>> Don't we need at-least 32GB + space for other early hash allocations
>>> BTW, My expectation was that 32TB would imply 32GB+32GB of large hash allocations early on
>> pgdat->node_spanned_pages >> 8 means that it allocates the size
>> of the memory on one node.
>> On a system with 2TB *16nodes, it will allocate 16*8GB = 128GB.
>> I am not sure if it can be minimised to >> 16 to make sure all
>> the architectures with different
>> memory size work well. And this is also mentioned in early
>> discussion for X86, so I choose >> 8.
>>
>> * From the code as the following:
>>
>> free_area_init_core ->
>> memmap_init->
>> update_defer_init
>> #define memmap_init(size, nid, zone, start_pfn) \
>> memmap_init_zone((size), (nid), (zone), (start_pfn), MEMMAP_EARLY)
>>
>> memmap_init_zone is based on a zone, but free_area_init_core will
>> help find the highest
>> zone on the node. And update_defer_init() get max initialised
>> memory on highest zone for a node to
>> reserve for early initialisation.
>>
>> static void __paginginit free_area_init_core(struct pglist_data *pgdat)
>> {
>> ...
>> for (j = 0; j < MAX_NR_ZONES; j++) {
>> ....
>> memmap_init(size, nid, j, zone_start_fn); //find
>> the highest zone on a node.
>> ...
>> }
>> }
>>
>> * From the dmesg log, after applying this patchset, it has
>> 123013440K(about 117GB),
>> which is enough for Dentry node hash table and Inode hash table in
>> this system.
>>
>> [ 0.000000] Memory: 123013440K/31739871232K available (8000K
>> kernel code, 1856K rwdata,
>> 3384K rodata, 6208K init, 2544K bss, 28531136K reserved, 0K cma-reserved)
>>
>> Thanks :)
>>
> Looks good! It seems the real benefit is for smaller systems - thanks for clarifying
> Please check if CMA is affected in any way
>
Sure, thanks.
> Acked-by: Balbir Singh <bsingharora@xxxxxxxxx>
>
> Balbir Singh.
--
Best Regards
-Li
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>