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.
> * 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.
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