Re: [PATCH v5 3/6] mm/cma: populate ZONE_CMA

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Thu, Sep 22, 2016 at 02:45:46PM +0900, Joonsoo Kim wrote:
> On Wed, Sep 21, 2016 at 11:20:11AM +0200, Vlastimil Babka wrote:
> > On 08/29/2016 07:07 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_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, so what happens on a system with multiple nodes? Each will have
> > its own ZONE_CMA, and all will have the same start pfn and spanned
> > pages?
> 
> Each of zone_start_pfn and spanned_pages are initialized in
> calculate_node_totalpages() which considers node boundary. So, they will
> have not the same start pfn and spanned pages. However, each would
> contain unnecessary holes.
> 
> > 
> > > /* 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.

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

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)) !=
+                               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) -