Add support for 16k pages

[jvoisin]

With 16384 pages:

size class	worst case internal fragmentation	slab slots	slab size	internal fragmentation for slabs
16	93.75%	256	16384	75.0%
32	46.88%	256	16384	50.0%
48	31.25%	256	16384	25.0%
64	23.44%	256	16384	0.0%
80	18.75%	204	16384	0.390625%
96	15.62%	170	16384	0.390625%
112	13.39%	146	16384	0.1953125%
128	11.72%	256	32768	0.0%
160	19.38%	204	32768	0.390625%
192	16.15%	256	49152	0.0%
224	13.84%	219	49152	0.1953125%
256	12.11%	256	65536	0.0%
320	19.69%	256	81920	0.0%
384	16.41%	256	98304	0.0%
448	14.06%	256	114688	0.0%
512	12.3%	256	131072	0.0%
640	19.84%	256	163840	0.0%
768	16.54%	256	196608	0.0%
896	14.17%	256	229376	0.0%
1024	12.4%	256	262144	0.0%
1280	19.92%	192	245760	0.0%
1536	16.6%	160	245760	0.0%
1792	14.23%	128	229376	0.0%
2048	12.45%	128	262144	0.0%
2560	19.96%	96	245760	0.0%
3072	16.63%	80	245760	0.0%
3584	14.26%	64	229376	0.0%
4096	12.48%	64	262144	0.0%
5120	19.98%	48	245760	0.0%
6144	16.65%	40	245760	0.0%
7168	14.27%	32	229376	0.0%
8192	12.49%	32	262144	0.0%
10240	19.99%	24	245760	0.0%
12288	16.66%	20	245760	0.0%
14336	14.28%	16	229376	0.0%
16384	12.49%	16	262144	0.0%
20480	20.0%	12	245760	0.0%
24576	16.66%	10	245760	0.0%
28672	14.28%	8	229376	0.0%
32768	12.5%	8	262144	0.0%
40960	20.0%	6	245760	0.0%
49152	16.66%	5	245760	0.0%
57344	14.28%	4	229376	0.0%
65536	12.5%	4	262144	0.0%
81920	20.0%	3	245760	0.0%
98304	16.67%	2	196608	0.0%
114688	14.28%	2	229376	0.0%
131072	12.5%	2	262144	0.0%

maximum bitmap size is 256-bit
maximum page span size is 16 (262144)

with 4k to compare:

size class	worst case internal fragmentation	slab slots	slab size	internal fragmentation for slabs
16	93.75%	256	4096	0.0%
32	46.88%	128	4096	0.0%
48	31.25%	85	4096	0.390625%
64	23.44%	64	4096	0.0%
80	18.75%	51	4096	0.390625%
96	15.62%	42	4096	1.5625%
112	13.39%	36	4096	1.5625%
128	11.72%	64	8192	0.0%
160	19.38%	51	8192	0.390625%
192	16.15%	64	12288	0.0%
224	13.84%	54	12288	1.5625%
256	12.11%	64	16384	0.0%
320	19.69%	64	20480	0.0%
384	16.41%	64	24576	0.0%
448	14.06%	64	28672	0.0%
512	12.3%	64	32768	0.0%
640	19.84%	64	40960	0.0%
768	16.54%	64	49152	0.0%
896	14.17%	64	57344	0.0%
1024	12.4%	64	65536	0.0%
1280	19.92%	16	20480	0.0%
1536	16.6%	16	24576	0.0%
1792	14.23%	16	28672	0.0%
2048	12.45%	16	32768	0.0%
2560	19.96%	8	20480	0.0%
3072	16.63%	8	24576	0.0%
3584	14.26%	8	28672	0.0%
4096	12.48%	8	32768	0.0%
5120	19.98%	8	40960	0.0%
6144	16.65%	8	49152	0.0%
7168	14.27%	8	57344	0.0%
8192	12.49%	8	65536	0.0%
10240	19.99%	6	61440	0.0%
12288	16.66%	5	61440	0.0%
14336	14.28%	4	57344	0.0%
16384	12.49%	4	65536	0.0%
20480	20.0%	2	40960	0.0%
24576	16.66%	2	49152	0.0%
28672	14.28%	2	57344	0.0%
32768	12.5%	2	65536	0.0%
40960	20.0%	1	40960	0.0%
49152	16.66%	1	49152	0.0%
57344	14.28%	1	57344	0.0%
65536	12.5%	1	65536	0.0%
81920	20.0%	1	81920	0.0%
98304	16.67%	1	98304	0.0%
114688	14.28%	1	114688	0.0%
131072	12.5%	1	131072	0.0%

maximum bitmap size is 256-bit
maximum page span size is 16 (65536)

This implements #213

[jvoisin]

This makes the testsuite pass on my local arm64 16k-pages test machine with make CONFIG_PAGE_SIZE=16384 clean test

[thestinger]

This is okay as an initial implementation but it really needs to be improved by having a larger or multi-level bitmap for handling the smallest sizes.

[jvoisin]

Yup, that's clearly a first step in the right direction, but nowhere near a complete proper implementation. I simply wanted to have the tests to work on my main machine :P

[jvoisin]

I don't think I'm comfortable enough with the codebase to implement multi-level bitmap in a nice way :/

[thestinger]

@jvoisin It could also just be a long bitmap with SIMD or something.