Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 21/25] Use allocation flags as an index to the zone watermark | Date | Wed, 22 Apr 2009 09:26:10 +0900 (JST) |
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> ALLOC_WMARK_MIN, ALLOC_WMARK_LOW and ALLOC_WMARK_HIGH determin whether > pages_min, pages_low or pages_high is used as the zone watermark when > allocating the pages. Two branches in the allocator hotpath determine which > watermark to use. This patch uses the flags as an array index and places > the three watermarks in a union with an array so it can be offset. This > means the flags can be used as an array index and reduces the branches > taken. > > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > Reviewed-by: Christoph Lameter <cl@linux-foundation.org> > --- > include/linux/mmzone.h | 8 +++++++- > mm/page_alloc.c | 18 ++++++++---------- > 2 files changed, 15 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index f82bdba..c1fa208 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -275,7 +275,13 @@ struct zone_reclaim_stat { > > struct zone { > /* Fields commonly accessed by the page allocator */ > - unsigned long pages_min, pages_low, pages_high; > + union { > + struct { > + unsigned long pages_min, pages_low, pages_high; > + }; > + unsigned long pages_mark[3]; > + }; > +
hmmm... I don't like union hack. Why can't we change all caller to use page_mark?
> /* > * We don't know if the memory that we're going to allocate will be freeable > * or/and it will be released eventually, so to avoid totally wasting several > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 376d848..e61867e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1157,10 +1157,13 @@ failed: > return NULL; > } > > -#define ALLOC_NO_WATERMARKS 0x01 /* don't check watermarks at all */ > -#define ALLOC_WMARK_MIN 0x02 /* use pages_min watermark */ > -#define ALLOC_WMARK_LOW 0x04 /* use pages_low watermark */ > -#define ALLOC_WMARK_HIGH 0x08 /* use pages_high watermark */ > +/* The WMARK bits are used as an index zone->pages_mark */ > +#define ALLOC_WMARK_MIN 0x00 /* use pages_min watermark */ > +#define ALLOC_WMARK_LOW 0x01 /* use pages_low watermark */ > +#define ALLOC_WMARK_HIGH 0x02 /* use pages_high watermark */ > +#define ALLOC_NO_WATERMARKS 0x08 /* don't check watermarks at all */ > +#define ALLOC_WMARK_MASK 0x07 /* Mask to get the watermark bits */
the mask only use two bit. but mask definition is three bit (0x07), why?
> + > #define ALLOC_HARDER 0x10 /* try to alloc harder */ > #define ALLOC_HIGH 0x20 /* __GFP_HIGH set */ > #ifdef CONFIG_CPUSETS > @@ -1463,12 +1466,7 @@ zonelist_scan: > > if (!(alloc_flags & ALLOC_NO_WATERMARKS)) { > unsigned long mark; > - if (alloc_flags & ALLOC_WMARK_MIN) > - mark = zone->pages_min; > - else if (alloc_flags & ALLOC_WMARK_LOW) > - mark = zone->pages_low; > - else > - mark = zone->pages_high; > + mark = zone->pages_mark[alloc_flags & ALLOC_WMARK_MASK]; > if (!zone_watermark_ok(zone, order, mark, > classzone_idx, alloc_flags)) { > if (!zone_reclaim_mode || > -- > 1.5.6.5 >
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