Re: [PATCH v3 3/6] mm/cma: populate ZONE_CMA

From: Joonsoo Kim
Date: Wed Jun 29 2016 - 03:58:07 EST

On Tue, Jun 28, 2016 at 07:23:23PM +0800, Chen Feng wrote:
> Hello,
>
> On 2016/6/23 10:52, Joonsoo Kim wrote:
> > 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.
> >
>
> The filesystem, inode map is also GFP_HIGHUSER_MOVABLE.
>
> SyS_write filemap_fault will also use cma memory.
>
> This may also make cma migrate failed. What's your idea on this type?

Purpose of this patchset is not improving success rate. It can be
solved separately if it is a real problem. Could you share how above
usage makes CMA migration failed and how long does it continue to
fail?

Thanks.