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This is causing a 2-node iperf3 client to server's network >>>> bandwidth to drop by 30% if we scale number of client-server pairs from 32 >>>> (where we achieved peak network bandwidth) to 64. >>>> >>>> To fix this issue, on allocation, reduce free_count by the exact number >>>> of pages that are allocated instead of halving it. >>> The present division by two appears to be somewhat randomly chosen. >>> And as far as I can tell, this patch proposes replacing that with >>> another somewhat random adjustment. >>> >>> What's the actual design here? What are we attempting to do and why, >>> and why is the proposed design superior to the present one? >> Cc Mel for the original design. >> >> IIUC, pcp->free_count is used to identify the consecutive, pure, large >> number of page freeing pattern. For that pattern, larger batch will be >> used to free pages from PCP to buddy to improve the performance. Mixed >> free/allocation pattern should not make pcp->free_count large, even if >> the number of the pages freed is much larger than that of the pages >> allocated in the long run. So, pcp->free_count decreases rapidly for >> the page allocation. >> >> Hi, Mel, please correct me if my understanding isn't correct. >> > hm, no Mel. > > Nikhil, please do continue to work on this - it seems that there will > be a significant benefit to retuning this. Hi Andrew, I have analyzed the performance of different memory-sensitive workloads for these two different ways to decrement pcp->free_count. I compared the score amongst v6.6 mainline, v6.7 mainline and v6.7 with our patch. For all the benchmarks, I used a 2-socket AMD server with 382 logical CPUs. Results I got are as follows: All scores are normalized with respect to v6.6 (base). For all the benchmarks below (iperf3, lmbench3 unix, netperf, redis, gups, xsbench), a higher score is better. iperf3 lmbench3 Unix 1-node netperf 2-node netperf (AF_UNIX) (SCTP_STREAM_MANY) (SCTP_STREAM_MANY) ------- -------------- ------------------ ------------------ v6.6 (base) 100 100 100 100 v6.7 69 113.2 99 98.59 v6.7 with my patch 100 112.1 100.3 101.16 redis standard redis core redis L3 Heavy Gups xsbench -------------- ---------- -------------- ---- ------- v6.6 (base) 100 100 100 100 100 v6.7 99.45 101.66 99.47 100 98.14 v6.7 with my patch 99.76 101.12 99.75 100 99.56 and for graph500, hashjoin, pagerank and Kbuild, a lower score is better. graph500 hashjoin hashjoin pagerank Kbuild (THP always) (THP never) --------- ------------ ----------- -------- ------ v6.6 (base) 100 100 100 100 100 v6.7 101.08 101.3 101.9 100 98.8 v6.7 with my patch 99.73 100 101.66 100 99.6 from these result I can conclude that this patch is performing better or as good as base v6.7 on almost all of these workloads.