On (02/22/16 09:25), Minchan Kim wrote:
[..]
> I tempted it several times with same reason you pointed out.
> But my worry was that if we increase ZS_MAX_ZSPAGE_ORDER, zram can
> consume more memory because we need several pages chain to populate
> just a object. Even, at that time, we didn't have compaction scheme
> so fragmentation of object in zspage is huge pain to waste memory.
well, the thing is -- we end up requesting less pages after all, so
zsmalloc has better chances to survive. for example, gcc5 compilation test
BASE
168 2720 0 1 115833 115831 77222
2
190 3072 0 1 109708 109707 82281
3
202 3264 0 5 1910 1895 1528
4
254 4096 0 0 380174 380174 380174
1
Total 44 285 1621495 1618234 891703
PATCHED
192 3104 1 0 3740 3737 2860
13
194 3136 0 1 7215 7208 5550
10
197 3184 1 0 11151 11150 8673
7
199 3216 0 1 9310 9304 7315
11
200 3232 0 1 4731 4717 3735
15
202 3264 0 1 8400 8396 6720
4
206 3328 0 1 22064 22051 17927
13
207 3344 0 1 4884 4877 3996
9
208 3360 0 1 4420 4415 3640
14
211 3408 0 1 11250 11246 9375
5
212 3424 1 0 3344 3343 2816
16
214 3456 0 2 7345 7329 6215
11
217 3504 0 1 10801 10797 9258
6
219 3536 0 1 5295 5289 4589
13
222 3584 0 0 6008 6008 5257
7
223 3600 0 1 1530 1518 1350
15
225 3632 0 1 3519 3514 3128
8
228 3680 0 1 3990 3985 3591
9
230 3712 0 2 2167 2151 1970
10
232 3744 1 2 1848 1835 1694
11
234 3776 0 2 1404 1384 1296
12
235 3792 0 2 672 654 624
13
236 3808 1 2 615 592 574
14
238 3840 1 2 1120 1098 1050
15
254 4096 0 0 241824 241824 241824
1
Total 129 489 1627756 1618193 850147
that's 891703 - 850147 = 41556 less pages. or 162MB less memory used.
41556 less pages means that zsmalloc had 41556 less chances to fail.
> Now, we have compaction facility so fragment of object might not
> be a severe problem but still painful to allocate 16 pages to store
> 3408 byte. So, if we want to increase ZS_MAX_ZSPAGE_ORDER,
> first of all, we should prepare dynamic creating of sub-page of
> zspage, I think and more smart compaction to minimize wasted memory.
well, I agree, but given that we allocate less pages, do we really want to
introduce this complexity at this point?
-ss
