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 12:32:37 -0500
From: Zi Yan <ziy@...dia.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 "\"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 15 Feb 2024, at 11:57, Vlastimil Babka wrote:

> 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?)

There is a __list_add_valid() performing list corruption checks.
>
>>
>> -	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.

Because compaction_free() indicates the page is not migrated and nr_migratepages
should be increased regardless.

Will fix it. Thanks.

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

--
Best Regards,
Yan, Zi

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