Re: [PATCH 11/12] hugetlb: batch TLB flushes when freeing vmemmap

[Muchun Song]

On 2023/8/26 03:04, Mike Kravetz wrote:
> From: Joao Martins <joao.m.martins@xxxxxxxxxx>
>
> Now that a list of pages is deduplicated at once, the TLB
> flush can be batched for all vmemmap pages that got remapped.
>
> Add a flags field and pass whether it's a bulk allocation or
> just a single page to decide to remap.
>
> The TLB flush is global as we don't have guarantees from caller
> that the set of folios is contiguous, or to add complexity in
> composing a list of kVAs to flush.
>
> Modified by Mike Kravetz to perform TLB flush on single folio if an
> error is encountered.
>
> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
>   mm/hugetlb_vmemmap.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 904a64fe5669..a2fc7b03ac6b 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -36,6 +36,7 @@ struct vmemmap_remap_walk {
>   	unsigned long		reuse_addr;
>   	struct list_head	*vmemmap_pages;
>   #define VMEMMAP_REMAP_ONLY_SPLIT	BIT(0)
> +#define	VMEMMAP_REMAP_BULK_PAGES	BIT(1)

We could reuse the flag (as I suggest VMEMMAP_SPLIT_WITHOUT_FLUSH)
proposed in the patch 10. When I saw this patch, I think the name
is not suitable, maybe VMEMMAP_WITHOUT_TLB_FLUSH is better.

Thanks.

>   	unsigned long		flags;
>   };
>   
> @@ -211,7 +212,8 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
>   			return ret;
>   	} while (pgd++, addr = next, addr != end);
>   
> -	if (!(walk->flags & VMEMMAP_REMAP_ONLY_SPLIT))
> +	if (!(walk->flags &
> +	      (VMEMMAP_REMAP_ONLY_SPLIT | VMEMMAP_REMAP_BULK_PAGES)))
>   		flush_tlb_kernel_range(start, end);
>   
>   	return 0;
> @@ -377,7 +379,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
>   		.remap_pte	= vmemmap_remap_pte,
>   		.reuse_addr	= reuse,
>   		.vmemmap_pages	= &vmemmap_pages,
> -		.flags		= 0,
> +		.flags		= !bulk_pages ? 0 : VMEMMAP_REMAP_BULK_PAGES,
>   	};
>   	int nid = page_to_nid((struct page *)start);
>   	gfp_t gfp_mask = GFP_KERNEL | __GFP_THISNODE | __GFP_NORETRY |
> @@ -427,6 +429,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
>   			.remap_pte	= vmemmap_restore_pte,
>   			.reuse_addr	= reuse,
>   			.vmemmap_pages	= &vmemmap_pages,
> +			.flags		= 0,
>   		};
>   
>   		vmemmap_remap_range(reuse, end, &walk);
> @@ -700,6 +703,8 @@ void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_l
>   	list_for_each_entry(folio, folio_list, lru)
>   		hugetlb_vmemmap_optimize_bulk(h, &folio->page, &vmemmap_pages);
>   
> +	flush_tlb_kernel_range(0, TLB_FLUSH_ALL);
> +
>   	free_vmemmap_page_list(&vmemmap_pages);
>   }
>