linux-kernel - Re: [PATCH 1/4] mm: thp: Return the correct value for change_huge

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Date:	Sat, 7 Mar 2015 12:13:27 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, xfs@....sgi.com,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 1/4] mm: thp: Return the correct value for change_huge_pmd

Looks obviously correct. The old code was just very wrong.

Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>

                     Linus


On Sat, Mar 7, 2015 at 7:20 AM, Mel Gorman <mgorman@...e.de> wrote:
> The wrong value is being returned by change_huge_pmd since commit
> 10c1045f28e8 ("mm: numa: avoid unnecessary TLB flushes when setting
> NUMA hinting entries") which allows a fallthrough that tries to adjust
> non-existent PTEs. This patch corrects it.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  mm/huge_memory.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index fc00c8cb5a82..194c0f019774 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1482,6 +1482,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>
>         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
>                 pmd_t entry;
> +               ret = 1;
>
>                 /*
>                  * Avoid trapping faults against the zero page. The read-only
> @@ -1490,11 +1491,10 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>                  */
>                 if (prot_numa && is_huge_zero_pmd(*pmd)) {
>                         spin_unlock(ptl);
> -                       return 0;
> +                       return ret;
>                 }
>
>                 if (!prot_numa || !pmd_protnone(*pmd)) {
> -                       ret = 1;
>                         entry = pmdp_get_and_clear_notify(mm, addr, pmd);
>                         entry = pmd_modify(entry, newprot);
>                         ret = HPAGE_PMD_NR;
> --
> 2.1.2
>
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