On Wednesday 19 September 2012 21:51:02 Andrew Morton wrote:
> On Fri, 14 Sep 2012 16:29:34 +0200
> Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> wrote:
>
> > * Add ALLOC_CMA alloc flag and pass it to [__]zone_watermark_ok()
> > (from Minchan Kim).
>
> What is its meaning and why was it added.
ALLOC_CMA flag means that allocation can use CMA areas to get free pages
from. Free CMA pages are accounted by system as normal free pages
(NR_FREE_PAGES) but they can be used only by movable type allocations
(otherwise they cannot be migrated once we want to do CMA allocation)
so we have to fix free_pages in __zone_watermark_ok() or the watermark
check will be too optimistic for unmovable allocations.
> > * During watermark check decrease available free pages number by
> > free CMA pages number if necessary (unmovable allocations cannot
> > use pages from CMA areas).
> >
> > ...
> >
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -231,6 +231,21 @@ enum zone_watermarks {
> > #define low_wmark_pages(z) (z->watermark[WMARK_LOW])
> > #define high_wmark_pages(z) (z->watermark[WMARK_HIGH])
> >
> > +/* The ALLOC_WMARK bits are used as an index to zone->watermark */
> > +#define ALLOC_WMARK_MIN WMARK_MIN
> > +#define ALLOC_WMARK_LOW WMARK_LOW
> > +#define ALLOC_WMARK_HIGH WMARK_HIGH
> > +#define ALLOC_NO_WATERMARKS 0x04 /* don't check watermarks at all */
> > +
> > +/* Mask to get the watermark bits */
> > +#define ALLOC_WMARK_MASK (ALLOC_NO_WATERMARKS-1)
> > +
> > +#define ALLOC_HARDER 0x10 /* try to alloc harder */
> > +#define ALLOC_HIGH 0x20 /* __GFP_HIGH set */
> > +#define ALLOC_CPUSET 0x40 /* check for correct cpuset */
> > +
>
> Unneeded newline.
>
> > +#define ALLOC_CMA 0x80
>
> All the other enumerations were documented. ALLOC_CMA was left
> undocumented, despite sorely needing documentation.
>
> > struct per_cpu_pages {
> > int count; /* number of pages in the list */
> > int high; /* high watermark, emptying needed */
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 4b902aa..36d79ea 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -868,6 +868,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
> > struct zoneref *z;
> > struct zone *zone;
> > int rc = COMPACT_SKIPPED;
> > + int alloc_flags = 0;
> >
> > /*
> > * Check whether it is worth even starting compaction. The order check is
> > @@ -879,6 +880,10 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
> >
> > count_vm_event(COMPACTSTALL);
> >
> > +#ifdef CONFIG_CMA
> > + if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> > + alloc_flags |= ALLOC_CMA;
>
> I find this rather obscure. What is the significance of
> MIGRATE_MOVABLE here? If it had been
>
> : if (allocflags_to_migratetype(gfp_mask) == MIGRATE_CMA)
> : alloc_flags |= ALLOC_CMA;
>
> then I'd have read straight past it. But it's unclear what's happening
> here. If we didn't have to resort to telepathy to understand the
> meaning of ALLOC_CMA, this wouldn't be so hard.
>
> > +#endif
> > /* Compact each zone in the list */
> > for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
> > nodemask) {
> > @@ -889,7 +894,8 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
> > rc = max(status, rc);
> >
> > /* If a normal allocation would succeed, stop compacting */
> > - if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
> > + if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
> > + alloc_flags))
> > break;
> > }
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 287f79d..5985cbf 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1519,19 +1519,6 @@ failed:
> > return NULL;
> > }
> >
> > -/* The ALLOC_WMARK bits are used as an index to zone->watermark */
> > -#define ALLOC_WMARK_MIN WMARK_MIN
> > -#define ALLOC_WMARK_LOW WMARK_LOW
> > -#define ALLOC_WMARK_HIGH WMARK_HIGH
> > -#define ALLOC_NO_WATERMARKS 0x04 /* don't check watermarks at all */
> > -
> > -/* Mask to get the watermark bits */
> > -#define ALLOC_WMARK_MASK (ALLOC_NO_WATERMARKS-1)
> > -
> > -#define ALLOC_HARDER 0x10 /* try to alloc harder */
> > -#define ALLOC_HIGH 0x20 /* __GFP_HIGH set */
> > -#define ALLOC_CPUSET 0x40 /* check for correct cpuset */
>
> Perhaps mm/internal.h wouild have been a better place to move these.
>
> > #ifdef CONFIG_FAIL_PAGE_ALLOC
> >
> > static struct {
> > @@ -1626,7 +1613,10 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> > min -= min / 2;
> > if (alloc_flags & ALLOC_HARDER)
> > min -= min / 4;
> > -
> > +#ifdef CONFIG_CMA
> > + if (!(alloc_flags & ALLOC_CMA))
> > + free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
>
> Again, the negated test looks weird or just wrong.
>
>
>
> Please do something to make this code more understandable.
Here is an incremental patch:
From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Subject: [PATCH] cma: fix watermark checking cleanup
Changes:
* document ALLOC_CMA
* add comment to __zone_watermark_ok()
* move ALLOC_* defines to mm/internal.h
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
---
include/linux/mmzone.h | 15 ---------------
mm/internal.h | 14 ++++++++++++++
mm/page_alloc.c | 1 +
3 files changed, 15 insertions(+), 15 deletions(-)
Index: b/include/linux/mmzone.h
===================================================================
--- a/include/linux/mmzone.h 2012-09-24 11:09:10.700992708 +0200
+++ b/include/linux/mmzone.h 2012-09-24 11:11:36.520992691 +0200
@@ -231,21 +231,6 @@ enum zone_watermarks {
#define low_wmark_pages(z) (z->watermark[WMARK_LOW])
#define high_wmark_pages(z) (z->watermark[WMARK_HIGH])
-/* The ALLOC_WMARK bits are used as an index to zone->watermark */
-#define ALLOC_WMARK_MIN WMARK_MIN
-#define ALLOC_WMARK_LOW WMARK_LOW
-#define ALLOC_WMARK_HIGH WMARK_HIGH
-#define ALLOC_NO_WATERMARKS 0x04 /* don't check watermarks at all */
-
-/* Mask to get the watermark bits */
-#define ALLOC_WMARK_MASK (ALLOC_NO_WATERMARKS-1)
-
-#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
-
struct per_cpu_pages {
int count; /* number of pages in the list */
int high; /* high watermark, emptying needed */
Index: b/mm/internal.h
===================================================================
--- a/mm/internal.h 2012-09-24 11:10:04.848992709 +0200
+++ b/mm/internal.h 2012-09-24 11:11:39.972992691 +0200
@@ -356,3 +356,17 @@ extern unsigned long vm_mmap_pgoff(struc
unsigned long, unsigned long);
extern void set_pageblock_order(void);
+
+/* The ALLOC_WMARK bits are used as an index to zone->watermark */
+#define ALLOC_WMARK_MIN WMARK_MIN
+#define ALLOC_WMARK_LOW WMARK_LOW
+#define ALLOC_WMARK_HIGH WMARK_HIGH
+#define ALLOC_NO_WATERMARKS 0x04 /* don't check watermarks at all */
+
+/* Mask to get the watermark bits */
+#define ALLOC_WMARK_MASK (ALLOC_NO_WATERMARKS-1)
+
+#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 */
Index: b/mm/page_alloc.c
===================================================================
--- a/mm/page_alloc.c 2012-09-24 11:12:22.212992717 +0200
+++ b/mm/page_alloc.c 2012-09-24 11:15:28.212992661 +0200
@@ -1614,6 +1614,7 @@ static bool __zone_watermark_ok(struct z
if (alloc_flags & ALLOC_HARDER)
min -= min / 4;
#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
--
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