[RFC PATCH 7/8] mm/vmalloc: Coalesce same page_shift mappings in vmap to avoid pgtable zigzag

[Dev Jain]

On 08/04/26 8:21 am, Barry Song (Xiaomi) wrote:
> For vmap(), detect pages with the same page_shift and map them in
> batches, avoiding the pgtable zigzag caused by per-page mapping.
> 
> Signed-off-by: Barry Song (Xiaomi) <baohua at kernel.org>
> ---

In patch 4, you eliminate the pagetable rewalk, and in patch 5,
you re-introduce it, then in this patch you eliminate it again.
So please just squash this into #5.

>  mm/vmalloc.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 6643ec0288cd..3c3b7217693a 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3551,6 +3551,8 @@ static int vmap_contig_pages_range(unsigned long addr, unsigned long end,
>  		pgprot_t prot, struct page **pages)
>  {
>  	unsigned int count = (end - addr) >> PAGE_SHIFT;
> +	unsigned int prev_shift = 0, idx = 0;
> +	unsigned long map_addr = addr;
>  	int err;
>  
>  	err = kmsan_vmap_pages_range_noflush(addr, end, prot, pages,
> @@ -3562,15 +3564,29 @@ static int vmap_contig_pages_range(unsigned long addr, unsigned long end,
>  		unsigned int shift = PAGE_SHIFT +
>  			get_vmap_batch_order(pages, count - i, i);
>  
> -		err = vmap_range_noflush(addr, addr + (1UL << shift),
> -				page_to_phys(pages[i]), prot, shift);
> -		if (err)
> -			goto out;
> +		if (!i)
> +			prev_shift = shift;
> +
> +		if (shift != prev_shift) {
> +			err = vmap_small_pages_range_noflush(map_addr, addr,
> +					prot, pages + idx,
> +					min(prev_shift, PMD_SHIFT));
> +			if (err)
> +				goto out;
> +			prev_shift = shift;
> +			map_addr = addr;
> +			idx = i;
> +		}
>  
>  		addr += 1UL << shift;
>  		i += 1U << (shift - PAGE_SHIFT);
>  	}
>  
> +	/* Remaining */
> +	if (map_addr < end)
> +		err = vmap_small_pages_range_noflush(map_addr, end,
> +				prot, pages + idx, min(prev_shift, PMD_SHIFT));
> +
>  out:
>  	flush_cache_vmap(addr, end);
>  	return err;