Messages in this thread | | | Date | Wed, 22 Apr 2009 11:23:33 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 21/25] Use allocation flags as an index to the zone watermark |
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On Wed, Apr 22, 2009 at 11:21:17AM +0100, Mel Gorman wrote: > On Wed, Apr 22, 2009 at 09:26:10AM +0900, KOSAKI Motohiro wrote: > > > 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? > > > > Because pages_min, pages_low and pages_high are such well understood concepts > and their current use is easy to userstand. It could all be changed to getters > and setters with a patch to update all call sites or having symbolic names > for the index and forcing the use of the array but when I started doing that, > the code looked worse to my eye, not better. The union is a relatively > small hack but well contained within the one place that cares. > > > > /* > > > * 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? > > > > I was thinking ALLOC_NO_WATERMARKS-1 and that all the lower bits must be > cleared and left the value of 0x08 to occupy same number of bits even though > that wasn't necessary. As suggested I'll change this to > > ALLOC_NO_WATERMARKS 0x04 > WMARK_MASK (1-ALLOC_NO_WATERMARKS) >
ALLOC_NO_WATERMARKS-1 obviously is what I meant
> > > > > + > > > #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 > > > > > > > > > > > -- > Mel Gorman > Part-time Phd Student Linux Technology Center > University of Limerick IBM Dublin Software Lab
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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