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From: Vlastimil Babka <vbabka@suse.cz>
To: Mel Gorman <mgorman@techsingularity.net>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Linux-MM <linux-mm@kvack.org>,
	Linux-FSDevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, Jan Kara <jack@suse.cz>,
	Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH 7/8] mm, Remove cold parameter from free_hot_cold_page*
Date: Thu, 19 Oct 2017 15:12:33 +0200
Message-ID: <9e260f57-b871-81bd-66ee-b08fff949c7c@suse.cz> (raw)
In-Reply-To: <20171018075952.10627-8-mgorman@techsingularity.net>

On 10/18/2017 09:59 AM, Mel Gorman wrote:
> Most callers users of free_hot_cold_page claim the pages being released are
> cache hot. The exception is the page reclaim paths where it is likely that
> enough pages will be freed in the near future that the per-cpu lists are
> going to be recycled and the cache hotness information is lost.

Maybe it would make sense for reclaim to skip pcplists? (out of scope of
this series, of course).

> As no one
> really cares about the hotness of pages being released to the allocator,
> just ditch the parameter.
> 
> The APIs are renamed to indicate that it's no longer about hot/cold pages. It
> should also be less confusing as there are subtle differences between them.
> __free_pages drops a reference and frees a page when the refcount reaches
> zero. free_hot_cold_page handled pages whose refcount was already zero
> which is non-obvious from the name. free_unref_page should be more obvious.
> 
> No performance impact is expected as the overhead is marginal. The parameter
> is removed simply because it is a bit stupid to have a useless parameter
> copied everywhere.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

A comment below, though.

...
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 167e163cf733..13582efc57a0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2590,7 +2590,7 @@ void mark_free_pages(struct zone *zone)
>  }
>  #endif /* CONFIG_PM */
>  
> -static bool free_hot_cold_page_prepare(struct page *page, unsigned long pfn)
> +static bool free_unref_page_prepare(struct page *page, unsigned long pfn)
>  {
>  	int migratetype;
>  
> @@ -2602,8 +2602,7 @@ static bool free_hot_cold_page_prepare(struct page *page, unsigned long pfn)
>  	return true;
>  }
>  
> -static void free_hot_cold_page_commit(struct page *page, unsigned long pfn,
> -				bool cold)
> +static void free_unref_page_commit(struct page *page, unsigned long pfn)
>  {
>  	struct zone *zone = page_zone(page);
>  	struct per_cpu_pages *pcp;
> @@ -2628,10 +2627,7 @@ static void free_hot_cold_page_commit(struct page *page, unsigned long pfn,
>  	}
>  
>  	pcp = &this_cpu_ptr(zone->pageset)->pcp;
> -	if (!cold)
> -		list_add(&page->lru, &pcp->lists[migratetype]);
> -	else
> -		list_add_tail(&page->lru, &pcp->lists[migratetype]);
> +	list_add_tail(&page->lru, &pcp->lists[migratetype]);

Did you intentionally use the cold version here? Patch 8/8 uses the hot
version in __rmqueue_pcplist() and that makes more sense to me. It
should be either negligible or better, not worse.

>  	pcp->count++;
>  	if (pcp->count >= pcp->high) {
>  		unsigned long batch = READ_ONCE(pcp->batch);

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  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-18  7:59 [PATCH 0/8] Follow-up for speed up page cache truncation v2 Mel Gorman
2017-10-18  7:59 ` [PATCH 1/8] mm, page_alloc: Enable/disable IRQs once when freeing a list of pages Mel Gorman
2017-10-18  9:02   ` Vlastimil Babka
2017-10-18 10:15     ` Mel Gorman
2017-10-18  7:59 ` [PATCH 2/8] mm, truncate: Do not check mapping for every page being truncated Mel Gorman
2017-10-19  8:11   ` Jan Kara
2017-10-18  7:59 ` [PATCH 3/8] mm, truncate: Remove all exceptional entries from pagevec under one lock Mel Gorman
2017-10-18  7:59 ` [PATCH 4/8] mm: Only drain per-cpu pagevecs once per pagevec usage Mel Gorman
2017-10-19  9:12   ` Vlastimil Babka
2017-10-19  9:33     ` Mel Gorman
2017-10-19 13:21       ` Vlastimil Babka
2017-10-18  7:59 ` [PATCH 5/8] mm, pagevec: Remove cold parameter for pagevecs Mel Gorman
2017-10-19  9:24   ` Vlastimil Babka
2017-10-18  7:59 ` [PATCH 6/8] mm: Remove cold parameter for release_pages Mel Gorman
2017-10-19  9:26   ` Vlastimil Babka
2017-10-18  7:59 ` [PATCH 7/8] mm, Remove cold parameter from free_hot_cold_page* Mel Gorman
2017-10-19 13:12   ` Vlastimil Babka [this message]
2017-10-19 15:43     ` Mel Gorman
2017-10-18  7:59 ` [PATCH 8/8] mm: Remove __GFP_COLD Mel Gorman
2017-10-19 13:18   ` Vlastimil Babka
2017-10-19 13:42   ` Vlastimil Babka
2017-10-19 14:32     ` Mel Gorman
  -- strict thread matches above, loose matches on Subject: below --
2017-10-12  9:30 [PATCH 0/8] Follow-up for speed up page cache truncation Mel Gorman
2017-10-12  9:31 ` [PATCH 7/8] mm, Remove cold parameter from free_hot_cold_page* Mel Gorman

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