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SubjectRe: [PATCH] mm: sparse: pass section_nr to section_mark_present
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On 01.07.21 17:41, 권오훈 wrote:
> On Thu, Jul 01, 2021 at 04:34:13PM +0200, David Hildenbrand wrote:
>> On 01.07.21 15:55, 권오훈 wrote:
>>> With CONFIG_SPARSEMEM_EXTREME enabled, __section_nr() which converts
>>> mem_section to section_nr could be costly since it iterates all
>>> sections to check if the given mem_section is in its range.
>>
>> It actually iterates all section roots.
>>
>>>
>>> On the other hand, __nr_to_section which converts section_nr to
>>> mem_section can be done in O(1).
>>>
>>> Let's pass section_nr instead of mem_section ptr to section_mark_present
>>> in order to reduce needless iterations.
>>
>> I'd expect this to be mostly noise, especially as we iterate section
>> roots and for most (smallish) machines we might just work on the lowest
>> section roots only.
>>
>> Can you actually observe an improvement regarding boot times?
>>
>> Anyhow, looks straight forward to me, although we might just reintroduce
>> similar patterns again easily if it's really just noise (see
>> find_memory_block() as used by). And it might allow for a nice cleanup
>> (see below).
>>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>>
>>
>> Can you send 1) a patch to convert find_memory_block() as well and 2) a
>> patch to rip out __section_nr() completely?
>>
>>>
>>> Signed-off-by: Ohhoon Kwon <ohoono.kwon@samsung.com>
>>> ---
>>> mm/sparse.c | 9 +++++----
>>> 1 file changed, 5 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/mm/sparse.c b/mm/sparse.c
>>> index 55c18aff3e42..4a2700e9a65f 100644
>>> --- a/mm/sparse.c
>>> +++ b/mm/sparse.c
>>> @@ -186,13 +186,14 @@ void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
>>> * those loops early.
>>> */
>>> unsigned long __highest_present_section_nr;
>>> -static void section_mark_present(struct mem_section *ms)
>>> +static void section_mark_present(unsigned long section_nr)
>>> {
>>> - unsigned long section_nr = __section_nr(ms);
>>> + struct mem_section *ms;
>>>
>>> if (section_nr > __highest_present_section_nr)
>>> __highest_present_section_nr = section_nr;
>>>
>>> + ms = __nr_to_section(section_nr);
>>> ms->section_mem_map |= SECTION_MARKED_PRESENT;
>>> }
>>>
>>> @@ -279,7 +280,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
>>> if (!ms->section_mem_map) {
>>> ms->section_mem_map = sparse_encode_early_nid(nid) |
>>> SECTION_IS_ONLINE;
>>> - section_mark_present(ms);
>>> + section_mark_present(section);
>>> }
>>> }
>>> }
>>> @@ -933,7 +934,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>>>
>>> ms = __nr_to_section(section_nr);
>>> set_section_nid(section_nr, nid);
>>> - section_mark_present(ms);
>>> + section_mark_present(section_nr);
>>>
>>> /* Align memmap to section boundary in the subsection case */
>>> if (section_nr_to_pfn(section_nr) != start_pfn)
>>>
>>
>>
>> --
>> Thanks,
>>
>> David / dhildenb
>>
> Dear David.
>
> I tried to check on time for memblocks_present, but when I tested with mobile
> phones with 8GB ram, the original binary took 0us either as well as the
> patched binary.
> I'm not sure how the results would differ on huge systems with bigger ram.
> I agree that it could turn out to be just a noise, as you expected.
>
> However as you also mentioned, the patches will be straight forward when all
> codes using __section_nr() are cleaned up nicely.
>
> Below are the two patches that you asked for.
> Please tell me if you need me to send the patches in separate e-mails.

Yes, please send them separately. Maybe sent all 3 patches combined in a
single series, so Andrew can pick them easily, and reviewers can review
more easily.

Thanks!

--
Thanks,

David / dhildenb

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