linux-kernel - Re: [PATCH v5 3/6] mm/cma: populate ZONE

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Date:   Thu, 22 Sep 2016 17:59:46 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, Laura Abbott <lauraa@...eaurora.org>,
        Minchan Kim <minchan@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/6] mm/cma: populate ZONE_CMA

On 09/22/2016 08:50 AM, Joonsoo Kim wrote:
> On Thu, Sep 22, 2016 at 02:45:46PM +0900, Joonsoo Kim wrote:
>> >
>> > > /* Free whole pageblock and set its migration type to MIGRATE_CMA. */
>> > > void __init init_cma_reserved_pageblock(struct page *page)
>> > > {
>> > > 	unsigned i = pageblock_nr_pages;
>> > >+	unsigned long pfn = page_to_pfn(page);
>> > > 	struct page *p = page;
>> > >+	int nid = page_to_nid(page);
>> > >+
>> > >+	/*
>> > >+	 * ZONE_CMA will steal present pages from other zones by changing
>> > >+	 * page links so page_zone() is changed. Before that,
>> > >+	 * we need to adjust previous zone's page count first.
>> > >+	 */
>> > >+	adjust_present_page_count(page, -pageblock_nr_pages);
>> > >
>> > > 	do {
>> > > 		__ClearPageReserved(p);
>> > > 		set_page_count(p, 0);
>> > >-	} while (++p, --i);
>> > >+
>> > >+		/* Steal pages from other zones */
>> > >+		set_page_links(p, ZONE_CMA, nid, pfn);
>> > >+	} while (++p, ++pfn, --i);
>> > >+
>> > >+	adjust_present_page_count(page, pageblock_nr_pages);
>> >
>> > This seems to assign pages to ZONE_CMA on the proper node, which is
>> > good. But then ZONE_CMA on multiple nodes will have unnecessary
>> > holes in the spanned pages, as each will contain only a subset.
>>
>> True, I will fix it and respin the series.
>
> I now realize that it's too late to send full series for next
> merge window. I will send full series after next merge window is closed.

I think there might still be rc8 thus another week.

> Anyway, I'd like to confirm that following incremental patch will solve
> your concern.

Yeah that should work, as long as single cma areas don't include multiple nodes?

> Thanks.
>
>
> ------>8--------------
>  mm/cma.c | 25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index d69bdf7..8375554 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -146,22 +146,29 @@ static int __init cma_init_reserved_areas(void)
>  {
>         int i;
>         struct zone *zone;
> -       unsigned long start_pfn = UINT_MAX, end_pfn = 0;
> +       pg_data_t *pgdat;
>
>         if (!cma_area_count)
>                 return 0;
>
> -       for (i = 0; i < cma_area_count; i++) {
> -               if (start_pfn > cma_areas[i].base_pfn)
> -                       start_pfn = cma_areas[i].base_pfn;
> -               if (end_pfn < cma_areas[i].base_pfn + cma_areas[i].count)
> -                       end_pfn = cma_areas[i].base_pfn + cma_areas[i].count;
> -       }
> +       for_each_online_pgdat(pgdat) {
> +               unsigned long start_pfn = UINT_MAX, end_pfn = 0;
>
> -       for_each_zone(zone) {
> -               if (!is_zone_cma(zone))
> +               for (i = 0; i < cma_area_count; i++) {
> +                       if (page_to_nid(pfn_to_page(cma_areas[i].base_pfn)) !=

We have pfn_to_nid() (although the implementation is just like this).

> +                               pgdat->node_id)
> +                               continue;
> +
> +                       start_pfn = min(start_pfn, cma_areas[i].base_pfn);
> +                       end_pfn = max(end_pfn, cma_areas[i].base_pfn +
> +                                               cma_areas[i].count);
> +               }
> +
> +               if (!end_pfn)
>                         continue;
>
> +               zone = &pgdat->node_zones[ZONE_CMA];
> +
>                 /* ZONE_CMA doesn't need to exceed CMA region */
>                 zone->zone_start_pfn = max(zone->zone_start_pfn, start_pfn);
>                 zone->spanned_pages = min(zone_end_pfn(zone), end_pfn) -
>