Re: [PATCH 2/2] mm: compaction: skip the memory hole rapidly when isolating free pages

[Huang, Ying]

Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:

> On 7/10/2023 2:11 PM, Huang, Ying wrote:
>> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>> 
>>> On my machine with below memory layout, and I can see it will take more
>>> time to skip the larger memory hole (range: 0x100000000 - 0x1800000000)
>>> when isolating free pages. So adding a new helper to skip the memory
>>> hole rapidly, which can reduce the time consumed from about 70us to less
>>> than 1us.
>>>
>>> [    0.000000] Zone ranges:
>>> [    0.000000]   DMA      [mem 0x0000000040000000-0x00000000ffffffff]
>>> [    0.000000]   DMA32    empty
>>> [    0.000000]   Normal   [mem 0x0000000100000000-0x0000001fa7ffffff]
>> The memory hole is at the beginning of zone NORMAL?  If so, should
>> zone
>
> No, the memory hole range is 0x1000000000 - 0x1800000000, and the
> normal zone is start from 0x100000000.
>
> I'm sorry I made a typo in the commit message, which confuses you. The
> memory hole range should be: 0x1000000000 - 0x1800000000. I updated
> the commit message to the following and addressed David's comment:

Got it!  Thanks for explanation!

> "
> Just like commit 9721fd82351d ("mm: compaction: skip memory hole rapidly
> when isolating migratable pages"), I can see it will also take more
> time to skip the larger memory hole (range: 0x1000000000 - 0x1800000000)
> when isolating free pages on my machine with below memory layout. So
> like commit 9721fd82351d, adding a new helper to skip the memory hole
> rapidly, which can reduce the time consumed from about 70us to less
> than 1us.

LGTM.

Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>

> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000040000000-0x00000000ffffffff]
> [    0.000000]   DMA32    empty
> [    0.000000]   Normal   [mem 0x0000000100000000-0x0000001fa7ffffff]
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000040000000-0x0000000fffffffff]
> [    0.000000]   node   0: [mem 0x0000001800000000-0x0000001fa3c7ffff]
> [    0.000000]   node   0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff]
> [    0.000000]   node   0: [mem 0x0000001fa4000000-0x0000001fa402ffff]
> [    0.000000]   node   0: [mem 0x0000001fa4030000-0x0000001fa40effff]
> [    0.000000]   node   0: [mem 0x0000001fa40f0000-0x0000001fa73cffff]
> [    0.000000]   node   0: [mem 0x0000001fa73d0000-0x0000001fa745ffff]
> [    0.000000]   node   0: [mem 0x0000001fa7460000-0x0000001fa746ffff]
> [    0.000000]   node   0: [mem 0x0000001fa7470000-0x0000001fa758ffff]
> [    0.000000]   node   0: [mem 0x0000001fa7590000-0x0000001fa7ffffff]
> "
>
>> NORMAL start at 0x1800000000?  And, the free pages will not be scanned
>> there?  Or my understanding were wrong. >
>>> [    0.000000] Movable zone start for each node
>>> [    0.000000] Early memory node ranges
>>> [    0.000000]   node   0: [mem 0x0000000040000000-0x0000000fffffffff]
>>> [    0.000000]   node   0: [mem 0x0000001800000000-0x0000001fa3c7ffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa4000000-0x0000001fa402ffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa4030000-0x0000001fa40effff]
>>> [    0.000000]   node   0: [mem 0x0000001fa40f0000-0x0000001fa73cffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa73d0000-0x0000001fa745ffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa7460000-0x0000001fa746ffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa7470000-0x0000001fa758ffff]
>>> [    0.000000]   node   0: [mem 0x0000001fa7590000-0x0000001fa7ffffff]
>>>
>>> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>> ---
>>>   mm/compaction.c | 30 +++++++++++++++++++++++++++++-
>>>   1 file changed, 29 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/mm/compaction.c b/mm/compaction.c
>>> index 43358efdbdc2..9641e2131901 100644
>>> --- a/mm/compaction.c
>>> +++ b/mm/compaction.c
>>> @@ -249,11 +249,31 @@ static unsigned long skip_offline_sections(unsigned long start_pfn)
>>>     	return 0;
>>>   }
>>> +
>>> +static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
>>> +{
>>> +	unsigned long start_nr = pfn_to_section_nr(start_pfn);
>>> +
>>> +	if (!start_nr || online_section_nr(start_nr))
>>> +		return 0;
>>> +
>>> +	while (start_nr-- > 0) {
>>> +		if (online_section_nr(start_nr))
>>> +			return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION - 1;
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>>   #else
>>>   static unsigned long skip_offline_sections(unsigned long start_pfn)
>>>   {
>>>   	return 0;
>>>   }
>>> +
>>> +static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
>>> +{
>>> +	return 0;
>>> +}
>>>   #endif
>>>     /*
>>> @@ -1668,8 +1688,16 @@ static void isolate_freepages(struct compact_control *cc)
>>>     		page = pageblock_pfn_to_page(block_start_pfn,
>>> block_end_pfn,
>>>   									zone);
>>> -		if (!page)
>>> +		if (!page) {
>>> +			unsigned long next_pfn;
>>> +
>>> +			next_pfn = skip_offline_sections_reverse(block_start_pfn);
>>> +			if (next_pfn)
>>> +				block_start_pfn = max(pageblock_start_pfn(next_pfn),
>>> +						      low_pfn);
>>> +
>>>   			continue;
>>> +		}
>>>     		/* Check the block is suitable for migration */
>>>   		if (!suitable_migration_target(cc, page))