Re: [discuss] Re: 32-bit dma allocations on 64-bit platforms

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Jun 24, 2004 at 03:11:30PM -0700, Andrew Morton wrote:
> After setting lower_zone_protection to 10:
> 
> Active:111515 inactive:65009 dirty:116 writeback:0 unstable:0 free:3290 slab:75489 mapped:52247 pagetables:446
> DMA free:4172kB min:16kB low:32kB high:48kB active:0kB inactive:0kB present:16384kB
> protections[]: 8 5156 5860
> Normal free:8736kB min:936kB low:1872kB high:2808kB active:352780kB inactive:224972kB present:901120kB
> protections[]: 0 468 1172
> HighMem free:252kB min:128kB low:256kB high:384kB active:93280kB inactive:35064kB present:130516kB
> protections[]: 0 0 64
> 
> It's a bit complex, and perhaps the relative levels of the various
> thresholds could be tightened up.

this is the algorithm I added to 2.4 to produce good protection levels (with
lower_zone_reserve_ratio supposedly tunable at boot time):

static int lower_zone_reserve_ratio[MAX_NR_ZONES-1] = { 256, 32 };


		zone->watermarks[j].min = mask;
		zone->watermarks[j].low = mask*2;
		zone->watermarks[j].high = mask*3;
		/* now set the watermarks of the lower zones in the "j" classzone */
		for (idx = j-1; idx >= 0; idx--) {
			zone_t * lower_zone = pgdat->node_zones + idx;
			unsigned long lower_zone_reserve;
			if (!lower_zone->size)
				continue;

			mask = lower_zone->watermarks[idx].min;
			lower_zone->watermarks[j].min = mask;
			lower_zone->watermarks[j].low = mask*2;
			lower_zone->watermarks[j].high = mask*3;

			/* now the brainer part */
			lower_zone_reserve = realsize / lower_zone_reserve_ratio[idx];
			lower_zone->watermarks[j].min += lower_zone_reserve;
			lower_zone->watermarks[j].low += lower_zone_reserve;
			lower_zone->watermarks[j].high += lower_zone_reserve;

			realsize += lower_zone->realsize;
		}

Your code must be inferior since it doesn't even allow to tune each zone
differently (you seems not to have a lower_zone_reserve_ratio[idx]). Not sure
why you dont' simply forward port the code from 2.4 instead of reinventing it.