[PATCH v2 0/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE

[PATCH v2 0/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

v2
o previous failure in linux-next turned out that it's not the problem of
this patchset. It was caused by the wrong assumption by specific
architecture.

lkml.kernel.org/r/20171114173719.GA28152@atomide.com

o add missing cache flush to the patch "ARM: CMA: avoid double mapping
to the CMA area if CONFIG_HIGHMEM = y"


This patchset is the follow-up of the discussion about the
"Introduce ZONE_CMA (v7)" [1]. Please reference it if more information
is needed.

In this patchset, the memory of the CMA area is managed by using
the ZONE_MOVABLE. Since there is another type of the memory in this zone,
we need to maintain a migratetype for the CMA memory to account
the number of the CMA memory. So, unlike previous patchset, there is
less deletion of the code.

Otherwise, there is no big change.

Motivation of this patchset is described in the commit description of
the patch "mm/cma: manage the memory of the CMA area by using
the ZONE_MOVABLE". Please refer it for more information.

This patchset is based on linux-next-20170822 plus
"mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE".

Thanks.

[1]: lkml.kernel.org/r/1491880640-9944-1-git-send-email-iamjoonsoo.kim@lge.com


Joonsoo Kim (3):
  mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE
  mm/cma: remove ALLOC_CMA
  ARM: CMA: avoid double mapping to the CMA area if CONFIG_HIGHMEM = y

 arch/arm/mm/dma-mapping.c      | 16 +++++++-
 include/linux/memory_hotplug.h |  3 --
 include/linux/mm.h             |  1 +
 mm/cma.c                       | 83 ++++++++++++++++++++++++++++++++++++------
 mm/compaction.c                |  4 +-
 mm/internal.h                  |  4 +-
 mm/page_alloc.c                | 83 +++++++++++++++++++++++++++---------------
 7 files changed, 145 insertions(+), 49 deletions(-)

-- 
2.7.4

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[PATCH v2 1/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

0. History

This patchset is the follow-up of the discussion about the
"Introduce ZONE_CMA (v7)" [1]. Please reference it if more information
is needed.

1. What does this patch do?

This patch changes the management way for the memory of the CMA area
in the MM subsystem. Currently, The memory of the CMA area is managed
by the zone where their pfn is belong to. However, this approach has
some problems since MM subsystem doesn't have enough logic to handle
the situation that different characteristic memories are in a single zone.
To solve this issue, this patch try to manage all the memory of
the CMA area by using the MOVABLE zone. In MM subsystem's point of view,
characteristic of the memory on the MOVABLE zone and the memory of
the CMA area are the same. So, managing the memory of the CMA area
by using the MOVABLE zone will not have any problem.

2. Motivation

There are some problems with current approach. See following.
Although these problem would not be inherent and it could be fixed without
this conception change, it requires many hooks addition in various
code path and it would be intrusive to core MM and would be really
error-prone. Therefore, I try to solve them with this new approach.
Anyway, following is the problems of the current implementation.

o CMA memory utilization

First, following is the freepage calculation logic in MM.

- For movable allocation: freepage = total freepage
- For unmovable allocation: freepage = total freepage - CMA freepage

Freepages on the CMA area is used after the normal freepages in the zone
where the memory of the CMA area is belong to are exhausted. At that moment
that the number of the normal freepages is zero, so

- For movable allocation: freepage = total freepage = CMA freepage
- For unmovable allocation: freepage = 0

If unmovable allocation comes at this moment, allocation request would
fail to pass the watermark check and reclaim is started. After reclaim,
there would exist the normal freepages so freepages on the CMA areas
would not be used.

FYI, there is another attempt [2] trying to solve this problem in lkml.
And, as far as I know, Qualcomm also has out-of-tree solution for this
problem.

o useless reclaim

There is no logic to distinguish CMA pages in the reclaim path. Hence,
CMA page is reclaimed even if the system just needs the page that can
be usable for the kernel allocation.

o atomic allocation failure

This is also related to the fallback allocation policy for the memory
of the CMA area. Consider the situation that the number of the normal
freepages is *zero* since the bunch of the movable allocation requests
come. Kswapd would not be woken up due to following freepage calculation
logic.

- For movable allocation: freepage = total freepage = CMA freepage

If atomic unmovable allocation request comes at this moment, it would
fails due to following logic.

- For unmovable allocation: freepage = total freepage - CMA freepage = 0

It was reported by Aneesh [3].

o useless compaction

Usual high-order allocation request is unmovable allocation request and
it cannot be served from the memory of the CMA area. In compaction,
migration scanner try to migrate the page in the CMA area and make
high-order page there. As mentioned above, it cannot be usable
for the unmovable allocation request so it's just waste.

3. Current approach and new approach

Current approach is that the memory of the CMA area is managed by the zone
where their pfn is belong to. However, these memory should be
distinguishable since they have a strong limitation. So, they are marked
as MIGRATE_CMA in pageblock flag and handled specially. However,
as mentioned in section 2, the MM subsystem doesn't have enough logic
to deal with this special pageblock so many problems raised.

New approach is that the memory of the CMA area is managed by
the MOVABLE zone. MM already have enough logic to deal with special zone
like as HIGHMEM and MOVABLE zone. So, managing the memory of the CMA area
by the MOVABLE zone just naturally work well because constraints
for the memory of the CMA area that the memory should always be migratable
is the same with the constraint for the MOVABLE zone.

There is one side-effect for the usability of the memory of the CMA area.
The use of MOVABLE zone is only allowed for a request with GFP_HIGHMEM &&
GFP_MOVABLE so now the memory of the CMA area is also only allowed for
this gfp flag. Before this patchset, a request with GFP_MOVABLE can use
them. IMO, It would not be a big issue since most of GFP_MOVABLE request
also has GFP_HIGHMEM flag. For example, file cache page and anonymous page.
However, file cache page for blockdev file is an exception. Request for it
has no GFP_HIGHMEM flag. There is pros and cons on this exception.
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 this case.

Note that there is no change in admin POV since this patchset is just
for internal implementation change in MM subsystem. Just one minor
difference for admin is that the memory stat for CMA area will be printed
in the MOVABLE zone. That's all.

4. Result

Following is the experimental result related to utilization problem.

8 CPUs, 1024 MB, VIRTUAL MACHINE
make -j16

<Before>
CMA area:               0 MB            512 MB
Elapsed-time:           92.4		186.5
pswpin:                 82		18647
pswpout:                160		69839

<After>
CMA        :            0 MB            512 MB
Elapsed-time:           93.1		93.4
pswpin:                 84		46
pswpout:                183		92

[1]: lkml.kernel.org/r/1491880640-9944-1-git-send-email-iamjoonsoo.kim@lge.com
[2]: https://lkml.org/lkml/2014/10/15/623
[3]: http://www.spinics.net/lists/linux-mm/msg100562.html

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 include/linux/memory_hotplug.h |  3 --
 include/linux/mm.h             |  1 +
 mm/cma.c                       | 83 ++++++++++++++++++++++++++++++++++++------
 mm/internal.h                  |  3 ++
 mm/page_alloc.c                | 55 +++++++++++++++++++++++++---
 5 files changed, 126 insertions(+), 19 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 58e110a..703069a 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -231,9 +231,6 @@ void put_online_mems(void);
 void mem_hotplug_begin(void);
 void mem_hotplug_done(void);
 
-extern void set_zone_contiguous(struct zone *zone);
-extern void clear_zone_contiguous(struct zone *zone);
-
 #else /* ! CONFIG_MEMORY_HOTPLUG */
 #define pfn_to_online_page(pfn)			\
 ({						\
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7661156..1206585 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2090,6 +2090,7 @@ extern void setup_per_cpu_pageset(void);
 
 extern void zone_pcp_update(struct zone *zone);
 extern void zone_pcp_reset(struct zone *zone);
+extern void setup_zone_pageset(struct zone *zone);
 
 /* page_alloc.c */
 extern int min_free_kbytes;
diff --git a/mm/cma.c b/mm/cma.c
index 0607729..a8062af 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -38,6 +38,7 @@
 #include <trace/events/cma.h>
 
 #include "cma.h"
+#include "internal.h"
 
 struct cma cma_areas[MAX_CMA_AREAS];
 unsigned cma_area_count;
@@ -108,23 +109,25 @@ static int __init cma_activate_area(struct cma *cma)
 	if (!cma->bitmap)
 		return -ENOMEM;
 
-	WARN_ON_ONCE(!pfn_valid(pfn));
-	zone = page_zone(pfn_to_page(pfn));
-
 	do {
 		unsigned j;
 
 		base_pfn = pfn;
+		if (!pfn_valid(base_pfn))
+			goto err;
+
+		zone = page_zone(pfn_to_page(base_pfn));
 		for (j = pageblock_nr_pages; j; --j, pfn++) {
-			WARN_ON_ONCE(!pfn_valid(pfn));
+			if (!pfn_valid(pfn))
+				goto err;
+
 			/*
-			 * alloc_contig_range requires the pfn range
-			 * specified to be in the same zone. Make this
-			 * simple by forcing the entire CMA resv range
-			 * to be in the same zone.
+			 * In init_cma_reserved_pageblock(), present_pages
+			 * is adjusted with assumption that all pages in
+			 * the pageblock come from a single zone.
 			 */
 			if (page_zone(pfn_to_page(pfn)) != zone)
-				goto not_in_zone;
+				goto err;
 		}
 		init_cma_reserved_pageblock(pfn_to_page(base_pfn));
 	} while (--i);
@@ -138,7 +141,7 @@ static int __init cma_activate_area(struct cma *cma)
 
 	return 0;
 
-not_in_zone:
+err:
 	pr_err("CMA area %s could not be activated\n", cma->name);
 	kfree(cma->bitmap);
 	cma->count = 0;
@@ -148,6 +151,41 @@ static int __init cma_activate_area(struct cma *cma)
 static int __init cma_init_reserved_areas(void)
 {
 	int i;
+	struct zone *zone;
+	pg_data_t *pgdat;
+
+	if (!cma_area_count)
+		return 0;
+
+	for_each_online_pgdat(pgdat) {
+		unsigned long start_pfn = UINT_MAX, end_pfn = 0;
+
+		zone = &pgdat->node_zones[ZONE_MOVABLE];
+
+		/*
+		 * In this case, we cannot adjust the zone range
+		 * since it is now maximum node span and we don't
+		 * know original zone range.
+		 */
+		if (populated_zone(zone))
+			continue;
+
+		for (i = 0; i < cma_area_count; i++) {
+			if (pfn_to_nid(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->zone_start_pfn = start_pfn;
+		zone->spanned_pages = end_pfn - start_pfn;
+	}
 
 	for (i = 0; i < cma_area_count; i++) {
 		int ret = cma_activate_area(&cma_areas[i]);
@@ -156,9 +194,32 @@ static int __init cma_init_reserved_areas(void)
 			return ret;
 	}
 
+	/*
+	 * Reserved pages for ZONE_MOVABLE are now activated and
+	 * this would change ZONE_MOVABLE's managed page counter and
+	 * the other zones' present counter. We need to re-calculate
+	 * various zone information that depends on this initialization.
+	 */
+	build_all_zonelists(NULL);
+	for_each_populated_zone(zone) {
+		if (zone_idx(zone) == ZONE_MOVABLE) {
+			zone_pcp_reset(zone);
+			setup_zone_pageset(zone);
+		} else
+			zone_pcp_update(zone);
+
+		set_zone_contiguous(zone);
+	}
+
+	/*
+	 * We need to re-init per zone wmark by calling
+	 * init_per_zone_wmark_min() but doesn't call here because it is
+	 * registered on core_initcall and it will be called later than us.
+	 */
+
 	return 0;
 }
-core_initcall(cma_init_reserved_areas);
+pure_initcall(cma_init_reserved_areas);
 
 /**
  * cma_init_reserved_mem() - create custom contiguous area from reserved memory
diff --git a/mm/internal.h b/mm/internal.h
index e6bd351..1cfa4c7 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -168,6 +168,9 @@ extern void post_alloc_hook(struct page *page, unsigned int order,
 					gfp_t gfp_flags);
 extern int user_min_free_kbytes;
 
+extern void set_zone_contiguous(struct zone *zone);
+extern void clear_zone_contiguous(struct zone *zone);
+
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
 
 /*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b120f24..eb5cdd5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1635,16 +1635,38 @@ 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_MOVABLE 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_MOVABLE, nid, pfn);
+	} while (++p, ++pfn, --i);
+
+	adjust_present_page_count(page, pageblock_nr_pages);
 
 	set_pageblock_migratetype(page, MIGRATE_CMA);
 
@@ -6066,6 +6088,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 {
 	enum zone_type j;
 	int nid = pgdat->node_id;
+	unsigned long node_end_pfn = 0;
 
 	pgdat_resize_init(pgdat);
 #ifdef CONFIG_NUMA_BALANCING
@@ -6093,9 +6116,13 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 		struct zone *zone = pgdat->node_zones + j;
 		unsigned long size, realsize, freesize, memmap_pages;
 		unsigned long zone_start_pfn = zone->zone_start_pfn;
+		unsigned long movable_size = 0;
 
 		size = zone->spanned_pages;
 		realsize = freesize = zone->present_pages;
+		if (zone_end_pfn(zone) > node_end_pfn)
+			node_end_pfn = zone_end_pfn(zone);
+
 
 		/*
 		 * Adjust freesize so that it accounts for how much memory
@@ -6144,12 +6171,30 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 		zone_seqlock_init(zone);
 		zone_pcp_init(zone);
 
-		if (!size)
+		/*
+		 * The size of the CMA area is unknown now so we need to
+		 * prepare the memory for the usemap at maximum.
+		 */
+		if (IS_ENABLED(CONFIG_CMA) && j == ZONE_MOVABLE &&
+			pgdat->node_spanned_pages) {
+			movable_size = node_end_pfn - pgdat->node_start_pfn;
+		}
+
+		if (!size && !movable_size)
 			continue;
 
 		set_pageblock_order();
-		setup_usemap(pgdat, zone, zone_start_pfn, size);
-		init_currently_empty_zone(zone, zone_start_pfn, size);
+		if (movable_size) {
+			zone->zone_start_pfn = pgdat->node_start_pfn;
+			zone->spanned_pages = movable_size;
+			setup_usemap(pgdat, zone,
+				pgdat->node_start_pfn, movable_size);
+			init_currently_empty_zone(zone,
+				pgdat->node_start_pfn, movable_size);
+		} else {
+			setup_usemap(pgdat, zone, zone_start_pfn, size);
+			init_currently_empty_zone(zone, zone_start_pfn, size);
+		}
 		memmap_init(size, nid, j, zone_start_pfn);
 	}
 }
@@ -7749,7 +7794,7 @@ void free_contig_range(unsigned long pfn, unsigned nr_pages)
 }
 #endif
 
-#ifdef CONFIG_MEMORY_HOTPLUG
+#if defined CONFIG_MEMORY_HOTPLUG || defined CONFIG_CMA
 /*
  * The zone indicated has a new number of managed_pages; batch sizes and percpu
  * page high values need to be recalulated.
-- 
2.7.4

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[PATCH v2 2/3] mm/cma: remove ALLOC_CMA

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Now, all reserved pages for CMA region are belong to the ZONE_MOVABLE
and it only serves for a request with GFP_HIGHMEM && GFP_MOVABLE.
Therefore, we don't need to maintain ALLOC_CMA at all.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 mm/compaction.c |  4 +---
 mm/internal.h   |  1 -
 mm/page_alloc.c | 28 +++-------------------------
 3 files changed, 4 insertions(+), 29 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 10cd757..b8c2388 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1450,14 +1450,12 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
 	 * if compaction succeeds.
 	 * For costly orders, we require low watermark instead of min for
 	 * compaction to proceed to increase its chances.
-	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
-	 * suitable migration targets
 	 */
 	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
 				low_wmark_pages(zone) : min_wmark_pages(zone);
 	watermark += compact_gap(order);
 	if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
-						ALLOC_CMA, wmark_target))
+						0, wmark_target))
 		return COMPACT_SKIPPED;
 
 	return COMPACT_CONTINUE;
diff --git a/mm/internal.h b/mm/internal.h
index 1cfa4c7..3e5dc95 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -498,7 +498,6 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 #define ALLOC_HARDER		0x10 /* try to alloc harder */
 #define ALLOC_HIGH		0x20 /* __GFP_HIGH set */
 #define ALLOC_CPUSET		0x40 /* check for correct cpuset */
-#define ALLOC_CMA		0x80 /* allow allocations from CMA areas */
 
 enum ttu_flags;
 struct tlbflush_unmap_batch;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index eb5cdd5..18df47e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2773,7 +2773,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
 		 * exists.
 		 */
 		watermark = min_wmark_pages(zone) + (1UL << order);
-		if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
+		if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
 			return 0;
 
 		__mod_zone_freepage_state(zone, -(1UL << order), mt);
@@ -3049,12 +3049,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 	}
 
 
-#ifdef CONFIG_CMA
-	/* If allocation can't use CMA areas don't use free CMA pages */
-	if (!(alloc_flags & ALLOC_CMA))
-		free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
-#endif
-
 	/*
 	 * Check watermarks for an order-0 allocation request. If these
 	 * are not met, then a high-order request also cannot go ahead
@@ -3081,10 +3075,8 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 		}
 
 #ifdef CONFIG_CMA
-		if ((alloc_flags & ALLOC_CMA) &&
-		    !list_empty(&area->free_list[MIGRATE_CMA])) {
+		if (!list_empty(&area->free_list[MIGRATE_CMA]))
 			return true;
-		}
 #endif
 		if (alloc_harder &&
 			!list_empty(&area->free_list[MIGRATE_HIGHATOMIC]))
@@ -3104,13 +3096,6 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
 		unsigned long mark, int classzone_idx, unsigned int alloc_flags)
 {
 	long free_pages = zone_page_state(z, NR_FREE_PAGES);
-	long cma_pages = 0;
-
-#ifdef CONFIG_CMA
-	/* If allocation can't use CMA areas don't use free CMA pages */
-	if (!(alloc_flags & ALLOC_CMA))
-		cma_pages = zone_page_state(z, NR_FREE_CMA_PAGES);
-#endif
 
 	/*
 	 * Fast check for order-0 only. If this fails then the reserves
@@ -3119,7 +3104,7 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
 	 * the caller is !atomic then it'll uselessly search the free
 	 * list. That corner case is then slower but it is harmless.
 	 */
-	if (!order && (free_pages - cma_pages) > mark + z->lowmem_reserve[classzone_idx])
+	if (!order && free_pages > mark + z->lowmem_reserve[classzone_idx])
 		return true;
 
 	return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
@@ -3735,10 +3720,6 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 	} else if (unlikely(rt_task(current)) && !in_interrupt())
 		alloc_flags |= ALLOC_HARDER;
 
-#ifdef CONFIG_CMA
-	if (gfpflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
-		alloc_flags |= ALLOC_CMA;
-#endif
 	return alloc_flags;
 }
 
@@ -4205,9 +4186,6 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
 	if (should_fail_alloc_page(gfp_mask, order))
 		return false;
 
-	if (IS_ENABLED(CONFIG_CMA) && ac->migratetype == MIGRATE_MOVABLE)
-		*alloc_flags |= ALLOC_CMA;
-
 	return true;
 }
 
-- 
2.7.4

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[PATCH v2 3/3] ARM: CMA: avoid double mapping to the CMA area if CONFIG_HIGHMEM = y

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

CMA area is now managed by the separate zone, ZONE_MOVABLE,
to fix many MM related problems. In this implementation, if
CONFIG_HIGHMEM = y, then ZONE_MOVABLE is considered as HIGHMEM and
the memory of the CMA area is also considered as HIGHMEM.
That means that they are considered as the page without direct mapping.
However, CMA area could be in a lowmem and the memory could have
direct mapping.

In ARM, when establishing a new mapping for DMA, direct mapping should
be cleared since two mapping with different cache policy could cause
unknown problem. With this patch, PageHighmem() for the CMA memory
located in lowmem returns true so that the function for DMA mapping
cannot notice whether it needs to clear direct mapping or not, correctly.
To handle this situation, this patch always clears direct mapping
for such CMA memory.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 arch/arm/mm/dma-mapping.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index ada8eb2..8c398fe 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -466,6 +466,12 @@ void __init dma_contiguous_early_fixup(phys_addr_t base, unsigned long size)
 void __init dma_contiguous_remap(void)
 {
 	int i;
+
+	if (!dma_mmu_remap_num)
+		return;
+
+	/* call flush_cache_all() since CMA area would be large enough */
+	flush_cache_all();
 	for (i = 0; i < dma_mmu_remap_num; i++) {
 		phys_addr_t start = dma_mmu_remap[i].base;
 		phys_addr_t end = start + dma_mmu_remap[i].size;
@@ -498,7 +504,15 @@ void __init dma_contiguous_remap(void)
 		flush_tlb_kernel_range(__phys_to_virt(start),
 				       __phys_to_virt(end));
 
-		iotable_init(&map, 1);
+		/*
+		 * All the memory in CMA region will be on ZONE_MOVABLE.
+		 * If that zone is considered as highmem, the memory in CMA
+		 * region is also considered as highmem even if it's
+		 * physical address belong to lowmem. In this case,
+		 * re-mapping isn't required.
+		 */
+		if (!is_highmem_idx(ZONE_MOVABLE))
+			iotable_init(&map, 1);
 	}
 }
 
-- 
2.7.4

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Re: [PATCH v2 0/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE

[Tony Lindgren]

* js1304@gmail.com <js1304@gmail.com> [171201 07:55]:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> v2
> o previous failure in linux-next turned out that it's not the problem of
> this patchset. It was caused by the wrong assumption by specific
> architecture.
> 
> lkml.kernel.org/r/20171114173719.GA28152@atomide.com

Thanks works me, I've sent a pull request for the related fix for
v4.15-rc cycle. So feel free to add for the whole series:

Tested-by: Tony Lindgren <tony@atomide.com>

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Re: [PATCH v2 0/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE

[Andrew Morton]

On Fri,  1 Dec 2017 16:53:03 +0900 js1304@gmail.com wrote:

> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> v2
> o previous failure in linux-next turned out that it's not the problem of
> this patchset. It was caused by the wrong assumption by specific
> architecture.
> 
> lkml.kernel.org/r/20171114173719.GA28152@atomide.com
> 
> o add missing cache flush to the patch "ARM: CMA: avoid double mapping
> to the CMA area if CONFIG_HIGHMEM = y"
> 
> 
> This patchset is the follow-up of the discussion about the
> "Introduce ZONE_CMA (v7)" [1]. Please reference it if more information
> is needed.
> 
> In this patchset, the memory of the CMA area is managed by using
> the ZONE_MOVABLE. Since there is another type of the memory in this zone,
> we need to maintain a migratetype for the CMA memory to account
> the number of the CMA memory. So, unlike previous patchset, there is
> less deletion of the code.
> 
> Otherwise, there is no big change.
> 
> Motivation of this patchset is described in the commit description of
> the patch "mm/cma: manage the memory of the CMA area by using
> the ZONE_MOVABLE". Please refer it for more information.
> 
> This patchset is based on linux-next-20170822 plus
> "mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE".

mhocko had issues with that patch which weren't addressed?
http://lkml.kernel.org/r/20170914132452.d5klyizce72rhjaa@dhcp22.suse.cz

> Thanks.
> 
> [1]: lkml.kernel.org/r/1491880640-9944-1-git-send-email-iamjoonsoo.kim@lge.com

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Re: [PATCH v2 0/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE

[Joonsoo Kim]

On Fri, Dec 08, 2017 at 02:37:19PM -0800, Andrew Morton wrote:
> On Fri,  1 Dec 2017 16:53:03 +0900 js1304@gmail.com wrote:
> 
> > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > 
> > v2
> > o previous failure in linux-next turned out that it's not the problem of
> > this patchset. It was caused by the wrong assumption by specific
> > architecture.
> > 
> > lkml.kernel.org/r/20171114173719.GA28152@atomide.com
> > 
> > o add missing cache flush to the patch "ARM: CMA: avoid double mapping
> > to the CMA area if CONFIG_HIGHMEM = y"
> > 
> > 
> > This patchset is the follow-up of the discussion about the
> > "Introduce ZONE_CMA (v7)" [1]. Please reference it if more information
> > is needed.
> > 
> > In this patchset, the memory of the CMA area is managed by using
> > the ZONE_MOVABLE. Since there is another type of the memory in this zone,
> > we need to maintain a migratetype for the CMA memory to account
> > the number of the CMA memory. So, unlike previous patchset, there is
> > less deletion of the code.
> > 
> > Otherwise, there is no big change.
> > 
> > Motivation of this patchset is described in the commit description of
> > the patch "mm/cma: manage the memory of the CMA area by using
> > the ZONE_MOVABLE". Please refer it for more information.
> > 
> > This patchset is based on linux-next-20170822 plus
> > "mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE".
> 
> mhocko had issues with that patch which weren't addressed?
> http://lkml.kernel.org/r/20170914132452.d5klyizce72rhjaa@dhcp22.suse.cz

Hello, Andrew.

Sorry for late response. I was on a long vacation.

I don't do anything on that patch yet. In fact, that patch isn't really
necessary to this patchset so I didn't include it into this patchset.

I will re-submit that patch after fixing the issue.

Thanks.

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