linux-kernel - Re: [PATCH v7 3/5] mm/hugetlb: add support for mempolicy MPOL_PREFERRED

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Date:   Fri, 6 Aug 2021 15:35:48 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, ying.huang@...el.com
Subject: Re: [PATCH v7 3/5] mm/hugetlb: add support for mempolicy
 MPOL_PREFERRED_MANY

On Tue 03-08-21 13:59:20, Feng Tang wrote:
> From: Ben Widawsky <ben.widawsky@...el.com>
> 
> Implement the missing huge page allocation functionality while obeying
> the preferred node semantics. This is similar to the implementation
> for general page allocation, as it uses a fallback mechanism to try
> multiple preferred nodes first, and then all other nodes.
> 
> [akpm: fix compling issue when merging with other hugetlb patch]
> [Thanks to 0day bot for catching the missing #ifdef CONFIG_NUMA issue]
> Link: https://lore.kernel.org/r/20200630212517.308045-12-ben.widawsky@intel.com
> Suggested-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> Co-developed-by: Feng Tang <feng.tang@...el.com>
> Signed-off-by: Feng Tang <feng.tang@...el.com>

ifdefery is just ugly as hell. One way to get rid of that would be to
provide a mpol_is_preferred_many() wrapper and hide the CONFIG_NUMA in
mempolicy.h. I haven't checked but this might help to remove some other
ifdefery as well.

I especially dislike the label hidden in the ifdef. You can get rid of
that by checking the page for NULL.

> ---
>  mm/hugetlb.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 95714fb28150..9279f6d478d9 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1166,7 +1166,20 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  
>  	gfp_mask = htlb_alloc_mask(h);
>  	nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
> +#ifdef CONFIG_NUMA
> +	if (mpol->mode == MPOL_PREFERRED_MANY) {
> +		page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
> +		if (page)
> +			goto check_reserve;
> +		/* Fallback to all nodes */
> +		nodemask = NULL;
> +	}
> +#endif
>  	page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
> +
> +#ifdef CONFIG_NUMA
> +check_reserve:
> +#endif
>  	if (page && !avoid_reserve && vma_has_reserves(vma, chg)) {
>  		SetHPageRestoreReserve(page);
>  		h->resv_huge_pages--;
> @@ -2147,6 +2160,21 @@ struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
>  	nodemask_t *nodemask;
>  
>  	nid = huge_node(vma, addr, gfp_mask, &mpol, &nodemask);
> +#ifdef CONFIG_NUMA
> +	if (mpol->mode == MPOL_PREFERRED_MANY) {
> +		gfp_t gfp = gfp_mask | __GFP_NOWARN;
> +
> +		gfp &=  ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
> +		page = alloc_surplus_huge_page(h, gfp, nid, nodemask, false);
> +		if (page) {
> +			mpol_cond_put(mpol);
> +			return page;
> +		}
> +
> +		/* Fallback to all nodes */
> +		nodemask = NULL;
> +	}
> +#endif
>  	page = alloc_surplus_huge_page(h, gfp_mask, nid, nodemask, false);
>  	mpol_cond_put(mpol);
>  
> -- 
> 2.14.1

-- 
Michal Hocko
SUSE Labs