Subject: Re: [PATCH V3 2/2] mm: THP page cache support for ppc64

From: "Kirill A. Shutemov" <[email-masked]>
Date: Mon, 14 Nov 2016 05:11:46 +0300

On Sun, Nov 13, 2016 at 08:30:25PM +0530, Aneesh Kumar K.V wrote:
> Add arch specific callback in the generic THP page cache code that will
> deposit and withdarw preallocated page table. Archs like ppc64 use
> this preallocated table to store the hash pte slot information.
> 
> Testing:
> kernel build of the patch series on tmpfs mounted with option huge=always
> 
> The related thp stat:
> thp_fault_alloc 72939
> thp_fault_fallback 60547
> thp_collapse_alloc 603
> thp_collapse_alloc_failed 0
> thp_file_alloc 253763
> thp_file_mapped 4251
> thp_split_page 51518
> thp_split_page_failed 1
> thp_deferred_split_page 73566
> thp_split_pmd 665
> thp_zero_page_alloc 3
> thp_zero_page_alloc_failed 0
> 
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>

One nit-pick below, but otherwise

Acked-by: Kirill A. Shutemov <[email-masked]>

> @@ -2975,6 +3004,13 @@ static int do_set_pmd(struct fault_env *fe, struct page *page)
>  	ret = 0;
>  	count_vm_event(THP_FILE_MAPPED);
>  out:
> +	/*
> +	 * If we are going to fallback to pte mapping, do a
> +	 * withdraw with pmd lock held.
> +	 */
> +	if (arch_needs_pgtable_deposit() && (ret == VM_FAULT_FALLBACK))

Parenthesis are redundant around ret check.

> +		fe->prealloc_pte = pgtable_trans_huge_withdraw(vma->vm_mm,
> +							       fe->pmd);
>  	spin_unlock(fe->ptl);
>  	return ret;
>  }

-- 
 Kirill A. Shutemov