Re: [RFC][PATCH v2 3/3] mm/zsmalloc: increase ZS_MAX_PAGES_PER_ZSPAGE
From: Sergey Senozhatsky <hidden>
Date: 2016-02-22 00:46:42
Also in:
lkml
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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>