linux-kernel - Re: [PATCH 11/13] mm: cleanup the hmm_vma_handle

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Date:   Tue, 30 Jul 2019 17:53:14 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Christoph Hellwig <hch@....de>
CC:     Jérôme Glisse <jglisse@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Ralph Campbell <rcampbell@...dia.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/13] mm: cleanup the hmm_vma_handle_pmd stub

On Tue, Jul 30, 2019 at 08:52:01AM +0300, Christoph Hellwig wrote:
> Stub out the whole function when CONFIG_TRANSPARENT_HUGEPAGE is not set
> to make the function easier to read.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
>  mm/hmm.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 4d3bd41b6522..f4e90ea5779f 100644
> +++ b/mm/hmm.c
> @@ -455,13 +455,10 @@ static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
>  				range->flags[HMM_PFN_VALID];
>  }
>  
> -static int hmm_vma_handle_pmd(struct mm_walk *walk,
> -			      unsigned long addr,
> -			      unsigned long end,
> -			      uint64_t *pfns,
> -			      pmd_t pmd)
> -{
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
> +		unsigned long end, uint64_t *pfns, pmd_t pmd)
> +{
>  	struct hmm_vma_walk *hmm_vma_walk = walk->private;
>  	struct hmm_range *range = hmm_vma_walk->range;
>  	struct dev_pagemap *pgmap = NULL;
> @@ -490,11 +487,14 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk,
>  		put_dev_pagemap(pgmap);
>  	hmm_vma_walk->last = end;
>  	return 0;
> -#else
> -	/* If THP is not enabled then we should never reach this 

This old comment says we should never get here

> +}
> +#else /* CONFIG_TRANSPARENT_HUGEPAGE */
> +static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
> +		unsigned long end, uint64_t *pfns, pmd_t pmd)
> +{
>  	return -EINVAL;

So could we just do
   #define hmm_vma_handle_pmd NULL

?

At the very least this seems like a WARN_ON too?

Jason