linux-kernel - Re: [PATCH v2 04/10] power: separate PageHighMem() and PageHighMemZone() use case

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Message-ID: <20200501122245.GA21897@infradead.org>
Date:   Fri, 1 May 2020 05:22:45 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     js1304@...il.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Laura Abbott <labbott@...hat.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Eric Biederman <ebiederm@...ssion.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, kernel-team@....com,
        Christoph Hellwig <hch@...radead.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 04/10] power: separate PageHighMem() and
 PageHighMemZone() use case

On Wed, Apr 29, 2020 at 12:26:37PM +0900, js1304@...il.com wrote:
> index 6598001..be759a6 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1227,7 +1227,7 @@ static struct page *saveable_highmem_page(struct zone *zone, unsigned long pfn)
>  	if (!page || page_zone(page) != zone)
>  		return NULL;
>  
> -	BUG_ON(!PageHighMem(page));
> +	BUG_ON(!PageHighMemZone(page));

The above check already checks for the highmem zone.  So if we want
to keep the BUG_ON it needs stay PageHighMem to make sense.  That being
said I'd rather remove it entirelẏ.

> -	BUG_ON(PageHighMem(page));
> +	BUG_ON(PageHighMemZone(page));

Same here.

> @@ -1529,7 +1529,7 @@ static unsigned long preallocate_image_pages(unsigned long nr_pages, gfp_t mask)
>  		if (!page)
>  			break;
>  		memory_bm_set_bit(&copy_bm, page_to_pfn(page));
> -		if (PageHighMem(page))
> +		if (PageHighMemZone(page))
>  			alloc_highmem++;
>  		else
>  			alloc_normal++;

I don't fully understand the log here.  Can Pavel or Rafael clarify
why swsupst would care about the exact zone?