Re: [PATCH RFC v6 0/5] Accelerate page migration with batch copying and hardware offload
From: Huang, Ying
Date: Tue Jul 14 2026 - 07:29:58 EST
Hi, Garg,
Thanks for updated patch.
Shivank Garg <shivankg@xxxxxxx> writes:
[snip]
>
> PERFORMANCE RESULTS:
> --------------------
>
> AMD EPYC 7713 (Zen 3), 2 sockets, 32 cores, SMT on,
> 1 NUMA node per socket, 256 GB/node, v7.2-rc1, DVFS=Performance, PTDMA
> (16 DMA channels).
>
> Benchmark: move_pages() syscall to move pages between two NUMA nodes.
>
> 1). Moving different sized folios such that total transfer size is constant
> (1GB), with different number of DMA channels. Throughput in GB/s.
>
> a. Baseline (vanilla kernel, single-threaded, serial folio_copy):
> ================================================================================
> 4K | 16K | 64K | 256K | 1M | 2M |
> ================================================================================
> 3.28±0.14 | 4.98±0.18 | 6.19±0.08 | 6.77±0.08 | 7.02±0.11 | 10.80±0.13 |
>
> b. DMA offload (Patched Kernel, dcbm driver, N DMA channels):
> ============================================================================================
> N channel| 4K | 16K | 64K | 256K | 1M | 2M |
> ============================================================================================
> 1 | 2.38±0.17 | 2.77±0.03 | 3.21±0.03 | 5.00±0.02 | 5.09±0.64 | 12.62±0.07 |
> 2 | 2.87±0.11 | 4.06±0.05 | 5.09±0.04 | 6.97±0.08 | 8.43±0.06 | 14.32±0.10 |
> 4 | 3.32±0.07 | 5.30±0.06 | 7.21±0.09 | 9.69±0.15 | 11.36±0.13 | 26.98±0.19 |
> 8 | 3.68±0.09 | 6.28±0.10 | 9.16±0.13 | 12.05±0.16 | 15.33±2.80 | 46.06±0.55 |
> 12 | 3.83±0.05 | 6.65±0.17 | 10.00±0.16 | 12.98±0.18 | 15.87±0.19 | 61.31±1.28 |
> 16 | 3.94±0.09 | 6.78±0.10 | 10.48±0.13 | 13.48±0.20 | 16.90±0.24 | 65.06±2.46 |
>
> 2). First-folio latency: custom tracepoints (in migrate_pages_batch enter/exit,
> migrate_folio_done) measure latency per migrate_pages_batch() call.
>
> Throughput (GB/s) and first-folio latency (us), median of 10 runs.
>
> a. Vanilla Kernel:
>
> NR_MAX_BATCHED_MIGRATION upstream default value is 512.
> --- Order 0 (4K folios) --- --- Order 9 (2M folios) ---
> n vanilla/cpu n vanilla/cpu
> (folios) GB/s | first(us) (folios) GB/s | first(us)
> -------------------------- --------------------------
> 1 0.03 | 24 1 6.86 | 204
> 4 0.13 | 30 4 8.68 | 191
> 8 0.27 | 27 8 7.92 | 207
> 16 0.43 | 34 16 6.77 | 234
> 64 1.12 | 51 64 10.44 | 179
> 256 1.67 | 166 256 10.43 | 181
> 512 1.98 | 255 512 10.55 | 179
> 2048 2.38 | 233
> 4096 2.42 | 168
> 16384 2.72 | 167
> 65536 3.00 | 156
> 262144 3.10 | 151
>
> b. Patched kernel:
> N = NR_MAX_BATCHED_MIGRATION (in pages), Total migrated data fixed at
> 1 GB. Change N with knob (just for testing) to measure impact of
> different max batched size.
>
> --- ORDER 0 (4K folios) ---
>
> N offload/dma1 offload/dma4 offload/dma16
> GB/s | first(us) GB/s | first(us) GB/s | first(us)
> ------------------------------------------------------------------------
> 512 2.21 | 628 3.29 | 275 3.25 | 245
> 1024 2.06 | 1271 3.21 | 601 3.36 | 518
> 2048 2.02 | 2646 3.00 | 1388 3.20 | 1110
> 4096 2.08 | 4832 3.17 | 2514 3.41 | 2175
> 8192 2.16 | 9253 3.14 | 4839 3.62 | 3592
> 16384 2.24 | 17543 3.23 | 9680 3.58 | 7144
> 32768 2.22 | 36408 3.26 | 19301 3.67 | 14524
> 65536 2.12 | 82572 3.24 | 38091 3.62 | 29835
> 131072 2.08 | 153669 3.17 | 79744 3.48 | 62157
> 262144 2.05 | 332297 2.97 | 175315 3.33 | 134774
>
> --- ORDER 9 (2M folios) ---
>
> N offload/dma1 offload/dma4 offload/dma16
> GB/s | first(us) GB/s | first(us) GB/s | first(us)
> ------------------------------------------------------------------------
> 512 11.74 | 160 11.71 | 160 11.75 | 159
> 1024 12.18 | 310 13.82 | 274 13.76 | 275
> 2048 12.39 | 612 25.55 | 290 25.69 | 289
> 4096 12.54 | 1211 26.25 | 564 42.36 | 334
> 8192 12.54 | 2421 26.82 | 1111 51.85 | 485
> 16384 12.61 | 4824 26.91 | 2209 54.26 | 925
> 32768 12.62 | 9652 27.04 | 4404 54.72 | 1942
> 65536 12.64 | 19287 26.95 | 8835 57.30 | 3535
> 131072 12.64 | 38824 26.95 | 17900 58.58 | 7747
> 262144 12.66 | 77610 26.95 | 35743 66.31 | 13801
>
> OPEN QUESTION:
> --------------
>
> The best batch size depends on the hardware, and bigger isn't always better.
> NR_MAX_BATCHED_MIGRATION decides how many pages we move at once.
> Higher batch size can help amortize the setup cost of migrator but
> increases the first-folio latency (the folio is inaccessible for this
> window).
Yes. This is an important parameter for the batched migration. We
really need more information from people who have workload information
to make a decision. Can you try to reach them?
Also, can we find a sweet point where we can archive higher throughput
without increasing latency too much (e.g., < 1ms)?
> Goals could be workload dependent, e.g. higher throughput versus
> same throughput under a bounded latency.
>
> Should this be tunable to accommodate different hardware and goals?
[snip]
---
Best Regards,
Huang, Ying