Huang, Ying <ying.huang@xxxxxxxxx> 于2024年1月9日周二 10:05写道： > > Kairui Song <ryncsn@xxxxxxxxx> writes: > > > From: Kairui Song <kasong@xxxxxxxxxxx> > > > > Currently, shmem uses cluster readahead for all swap backends. Cluster > > readahead is not a good solution for ramdisk based device (ZRAM) at all. > > > > After switching to the new helper, most benchmarks showed a good result: > > > > - Single file sequence read: > > perf stat --repeat 20 dd if=/tmpfs/test of=/dev/null bs=1M count=8192 > > (/tmpfs/test is a zero filled file, using brd as swap, 4G memcg limit) > > Before: 22.248 +- 0.549 > > After: 22.021 +- 0.684 (-1.1%) > > > > - Random read stress test: > > fio -name=tmpfs --numjobs=16 --directory=/tmpfs \ > > --size=256m --ioengine=mmap --rw=randread --random_distribution=random \ > > --time_based --ramp_time=1m --runtime=5m --group_reporting > > (using brd as swap, 2G memcg limit) > > > > Before: 1818MiB/s > > After: 1888MiB/s (+3.85%) > > > > - Zipf biased random read stress test: > > fio -name=tmpfs --numjobs=16 --directory=/tmpfs \ > > --size=256m --ioengine=mmap --rw=randread --random_distribution=zipf:1.2 \ > > --time_based --ramp_time=1m --runtime=5m --group_reporting > > (using brd as swap, 2G memcg limit) > > > > Before: 31.1GiB/s > > After: 32.3GiB/s (+3.86%) > > > > So cluster readahead doesn't help much even for single sequence read, > > and for random stress test, the performance is better without it. > > > > Considering both memory and swap device will get more fragmented > > slowly, and commonly used ZRAM consumes much more CPU than plain > > ramdisk, false readahead could occur more frequently and waste > > more CPU. Direct SWAP is cheaper, so use the new helper and skip > > read ahead for SWP_SYNCHRONOUS_IO device. > > It's good to take advantage of swap_direct (no readahead). I also hopes > we can take advantage of VMA based swapin if shmem is accessed via mmap. > That appears possible. Good idea, that should be doable, will update the series.
