Re: [PATCH v3 3/6] mm/cma: populate ZONE_CMA
From: Joonsoo Kim
Date: Wed Jun 22 2016 - 22:50:10 EST
On Wed, Jun 22, 2016 at 05:23:06PM +0800, Chen Feng wrote:
> Hello,
>
> On 2016/5/26 14:22, js1304@xxxxxxxxx wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> >
> > 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@xxxxxxx>
> > ---
> > include/linux/memory_hotplug.h | 3 ---
> > mm/cma.c | 41 +++++++++++++++++++++++++++++++++++++++++
> > mm/internal.h | 3 +++
> > mm/page_alloc.c | 26 ++++++++++++++++++++++++--
> > 4 files changed, 68 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> > index a864d79..6fde69b 100644
> > --- a/include/linux/memory_hotplug.h
> > +++ b/include/linux/memory_hotplug.h
> > @@ -198,9 +198,6 @@ 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 */
> > /*
> > * Stub functions for when hotplug is off
> > diff --git a/mm/cma.c b/mm/cma.c
> > index ea506eb..8684f50 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;
> > @@ -145,6 +146,11 @@ 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++) {
> > int ret = cma_activate_area(&cma_areas[i]);
> > @@ -153,6 +159,41 @@ static int __init cma_init_reserved_areas(void)
> > return ret;
> > }
> >
> > + 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;
> > + }
> > +
> > + /*
> > + * Reserved pages for ZONE_CMA are now activated and this would change
> > + * ZONE_CMA's managed page counter and other zone's present counter.
> > + * We need to re-calculate various zone information that depends on
> > + * this initialization.
> > + */
> > + build_all_zonelists(NULL, NULL);
> > + for_each_populated_zone(zone) {
> > + 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 module_init and it will be called later than us.
> > + */
> > +
> > return 0;
> > }
> > core_initcall(cma_init_reserved_areas);
> > diff --git a/mm/internal.h b/mm/internal.h
> > index b6ead95..4c37234 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -155,6 +155,9 @@ extern void __free_pages_bootmem(struct page *page, unsigned long pfn,
> > extern void prep_compound_page(struct page *page, unsigned int order);
> > 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 0197d5d..796b271 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1572,16 +1572,38 @@ 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);
> >
> > 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);
> >
> > set_pageblock_migratetype(page, MIGRATE_CMA);
>
> The ZONE_CMA should depends on sparse_mem.
>
> Because the zone size is not fixed when init the buddy core.
> The pageblock_flags will be NULL when setup_usemap.
Before setup_usemap(), range of ZONE_CMA is set conservatively, from
min_start_pfn of the node to max_end_pfn of the node. So,
pageblock_flags will be allocated and assigned properly.
Unfortunately, I found a bug for FLATMEM system. If you'd like to
test ZONE_CMA on FLATMEM system, please apply below one.
Thanks.
------------>8------------
diff --git a/mm/cma.c b/mm/cma.c
index 0c1a72f..6cd2973 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -168,13 +168,6 @@ static int __init cma_init_reserved_areas(void)
return 0;
for (i = 0; i < cma_area_count; i++) {
- int ret = cma_activate_area(&cma_areas[i]);
-
- if (ret)
- return ret;
- }
-
- 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)
@@ -191,6 +184,13 @@ static int __init cma_init_reserved_areas(void)
zone->zone_start_pfn;
}
+ for (i = 0; i < cma_area_count; i++) {
+ int ret = cma_activate_area(&cma_areas[i]);
+
+ if (ret)
+ return ret;
+ }
+
/*
* Reserved pages for ZONE_CMA are now activated and this would change
* ZONE_CMA's managed page counter and other zone's present counter.
--
1.9.1