linux-kernel - Re: [PATCH v5 2/3] mm/compaction: add support for >0 order folio memory compaction.

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Date: Thu, 15 Feb 2024 17:57:42 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: "Huang, Ying" <ying.huang@...el.com>, Ryan Roberts
 <ryan.roberts@....com>, Andrew Morton <akpm@...ux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 David Hildenbrand <david@...hat.com>, "Yin, Fengwei"
 <fengwei.yin@...el.com>, Yu Zhao <yuzhao@...gle.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Johannes Weiner <hannes@...xchg.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Kemeng Shi <shikemeng@...weicloud.com>,
 Mel Gorman <mgorman@...hsingularity.net>, Rohan Puri
 <rohan.puri15@...il.com>, Mcgrof Chamberlain <mcgrof@...nel.org>,
 Adam Manzanares <a.manzanares@...sung.com>,
 "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: Re: [PATCH v5 2/3] mm/compaction: add support for >0 order folio
 memory compaction.

On 2/14/24 23:04, Zi Yan wrote:
> @@ -1849,10 +1857,22 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
>  static void compaction_free(struct folio *dst, unsigned long data)
>  {
>  	struct compact_control *cc = (struct compact_control *)data;
> +	int order = folio_order(dst);
> +	struct page *page = &dst->page;
> +
> +	if (folio_put_testzero(dst)) {
> +		free_pages_prepare_fpi_none(page, order);
> +
> +		INIT_LIST_HEAD(&dst->lru);

(is this even needed? I think the state of first parameter of list_add() is
never expected to be in particular state?)

>  
> -	list_add(&dst->lru, &cc->freepages);
> -	cc->nr_freepages++;
> -	cc->nr_migratepages += 1 << folio_order(dst);
> +		list_add(&dst->lru, &cc->freepages[order]);
> +		cc->nr_freepages += 1 << order;
> +		cc->nr_migratepages += 1 << order;

Hm actually this increment of nr_migratepages should happen even if we lost
the free page.

> +	}
> +	/*
> +	 * someone else has referenced the page, we cannot take it back to our
> +	 * free list.
> +	 */
>  }