linux-kernel - Re: [PATCH] mm/page_alloc: skip THP-sized PCP list when allocating non-CMA THP-sized page

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Date: Tue, 4 Jun 2024 20:01:54 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: yangge1116@....com, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, liuzixing@...on.cn,
 Johannes Weiner <hannes@...xchg.org>, Vlastimil Babka <vbabka@...e.cz>,
 Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH] mm/page_alloc: skip THP-sized PCP list when allocating
 non-CMA THP-sized page

Cc Johannes, Zi and Vlastimil.

On 2024/6/4 17:14, yangge1116@....com wrote:
> From: yangge <yangge1116@....com>
> 
> Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for
> THP-sized allocations") no longer differentiates the migration type
> of pages in THP-sized PCP list, it's possible to get a CMA page from
> the list, in some cases, it's not acceptable, for example, allocating
> a non-CMA page with PF_MEMALLOC_PIN flag returns a CMA page.
> 
> The patch forbids allocating non-CMA THP-sized page from THP-sized
> PCP list to avoid the issue above.
> 
> Fixes: 5d0a661d808f ("mm/page_alloc: use only one PCP list for THP-sized allocations")
> Signed-off-by: yangge <yangge1116@....com>
> ---
>   mm/page_alloc.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2e22ce5..0bdf471 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2987,10 +2987,20 @@ struct page *rmqueue(struct zone *preferred_zone,
>   	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
>   
>   	if (likely(pcp_allowed_order(order))) {
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +		if (!IS_ENABLED(CONFIG_CMA) || alloc_flags & ALLOC_CMA ||
> +						order != HPAGE_PMD_ORDER) {

Seems you will also miss the non-CMA THP from the PCP, so I wonder if we 
can add a migratetype comparison in __rmqueue_pcplist(), and if it's not 
suitable, then fallback to buddy?

> +			page = rmqueue_pcplist(preferred_zone, zone, order,
> +						migratetype, alloc_flags);
> +			if (likely(page))
> +				goto out;
> +		}
> +#else
>   		page = rmqueue_pcplist(preferred_zone, zone, order,
>   				       migratetype, alloc_flags);
>   		if (likely(page))
>   			goto out;
> +#endif
>   	}
>   
>   	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,