Messages in this thread | | | Subject | Re: [PATCH v4 2/5] mm/cma: populate ZONE_CMA | From | Vlastimil Babka <> | Date | Fri, 19 Aug 2016 13:20:13 +0200 |
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On 08/09/2016 08:39 AM, js1304@gmail.com wrote: > From: Joonsoo Kim <iamjoonsoo.kim@lge.com> > > Until now, reserved pages for CMA are managed in the ordinary zones > where page's pfn are belong to. This approach has numorous problems > and fixing them isn't easy. (It is mentioned on previous patch.) > To fix this situation, ZONE_CMA is introduced in previous patch, but, > not yet populated. This patch implement population of ZONE_CMA > by stealing reserved pages from the ordinary zones. > > Unlike previous implementation that kernel allocation request with > __GFP_MOVABLE could be serviced from CMA region, allocation request only > with GFP_HIGHUSER_MOVABLE can be serviced from CMA region in the new > approach. This is an inevitable design decision to use the zone > implementation because ZONE_CMA could contain highmem. Due to this > decision, ZONE_CMA will work like as ZONE_HIGHMEM or ZONE_MOVABLE. > > I don't think it would be a problem because most of file cache pages > and anonymous pages are requested with GFP_HIGHUSER_MOVABLE. It could > be proved by the fact that there are many systems with ZONE_HIGHMEM and > they work fine. Notable disadvantage is that we cannot use these pages > for blockdev file cache page, because it usually has __GFP_MOVABLE but > not __GFP_HIGHMEM and __GFP_USER. But, in this case, there is pros and > cons. In my experience, blockdev file cache pages are one of the top > reason that causes cma_alloc() to fail temporarily. So, we can get more > guarantee of cma_alloc() success by discarding that case. > > Implementation itself is very easy to understand. Steal when cma area is > initialized and recalculate various per zone stat/threshold. > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
[...]
> @@ -145,6 +145,28 @@ err: > static int __init cma_init_reserved_areas(void) > { > int i; > + struct zone *zone; > + unsigned long start_pfn = UINT_MAX, end_pfn = 0; > + > + 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_populated_zone(zone) { > + if (!is_zone_cma(zone)) > + continue; > + > + /* 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) - > + zone->zone_start_pfn;
Hmm is this a dead code? for_each_populated_zone() will skip zones where zone->present_pages is 0, which is AFAICS the result for ZONE_CMA after it's initialized by calculate_node_totalpages() (after Patch 1/5). The present_pages seem to be only increased later in this function by cma_activate_area() -> init_cma_reserved_pageblock().
> + } > > for (i = 0; i < cma_area_count; i++) { > int ret = cma_activate_area(&cma_areas[i]); > @@ -153,6 +175,24 @@ static int __init cma_init_reserved_areas(void) > return ret; > } >
[...]
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index f6c4358..352096e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1600,16 +1600,38 @@ void __init page_alloc_init_late(void) > } > > #ifdef CONFIG_CMA > +static void __init adjust_present_page_count(struct page *page, long count) > +{ > + struct zone *zone = page_zone(page); > + > + /* We don't need to hold a lock since it is boot-up process */ > + zone->present_pages += count; > +} > + > /* 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);
So in previous version I said this (and you replied):
>> > Ideally, zone's start_pfn and spanned_pages should be also adjusted >> > if we stole from the beginning/end (which I suppose should be quite >> > common?). > > It would be possible. Maybe, there is a reason I didn't do that but I > don't remember it. I will think more.
What's the outcome? :) Is stealing from beginning/end of zone common for CMA? Are we losing zone->contiguous and add iterations to compaction scanner needlessly?
Thanks.
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