Re: [PATCH v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD

[Oleg Nesterov]

On 08/07, Song Liu wrote:
>
> @@ -399,7 +399,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
>  		spin_unlock(ptl);
>  		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
>  	}
> -	if (flags & FOLL_SPLIT) {
> +	if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) {
>  		int ret;
>  		page = pmd_page(*pmd);
>  		if (is_huge_zero_page(page)) {
> @@ -408,7 +408,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
>  			split_huge_pmd(vma, pmd, address);
>  			if (pmd_trans_unstable(pmd))
>  				ret = -EBUSY;
> -		} else {
> +		} else if (flags & FOLL_SPLIT) {
>  			if (unlikely(!try_get_page(page))) {
>  				spin_unlock(ptl);
>  				return ERR_PTR(-ENOMEM);
> @@ -420,6 +420,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
>  			put_page(page);
>  			if (pmd_none(*pmd))
>  				return no_page_table(vma, flags);
> +		} else {  /* flags & FOLL_SPLIT_PMD */
> +			spin_unlock(ptl);
> +			split_huge_pmd(vma, pmd, address);
> +			ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;
>  		}

Can't resist, let me repeat that I do not like this patch because imo
it complicates this code for no reason.

But I can't insist and of course I could miss something.

Oleg.