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

[David Hildenbrand]

On 07.07.23 10:51, Baolin Wang wrote:
> 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.

Can you clarify how this relates to the previous commit and mention that 
commit?

> [    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]
>
> 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))


LGTM

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb