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

[Baolin Wang]

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:

"
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.

[    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))