Re: [PATCH 7/9] mm, swap: remove contention workaround for swap cache

[Chris Li <chrisl@kernel.org>]

On Sun, Aug 31, 2025 at 8:55 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> So I tried to run some HDD test for many rounds, basically doing the
> test in the URL below manually. Test is done using nr_task = 8. The
> HDD swap partition size is 8G.
>
> Do the preparation following:
> https://github.com/intel/lkp-tests/blob/master/setup/swapin_setup
> (Make usemem hold 8G memory and push them to swap)
>
> And do the test with:
> https://github.com/intel/lkp-tests/blob/master/programs/swapin/run
> (Use SIGUSR1 to make usemem to read its memory and swapin)
>
> Before this patch:
> Test run 1:
> 1073741824 bytes / 878662493 usecs = 1193 KB/s
> 33019 usecs to free memory
> 1073741824 bytes / 891315681 usecs = 1176 KB/s
> 35144 usecs to free memory
> 1073741824 bytes / 898801090 usecs = 1166 KB/s
> 36305 usecs to free memory
> 1073741824 bytes / 925899753 usecs = 1132 KB/s
> 20498 usecs to free memory
> 1073741824 bytes / 927522592 usecs = 1130 KB/s
> 34397 usecs to free memory
> 1073741824 bytes / 928164994 usecs = 1129 KB/s
> 35908 usecs to free memory
> 1073741824 bytes / 929890294 usecs = 1127 KB/s
> 35014 usecs to free memory
> 1073741824 bytes / 929997808 usecs = 1127 KB/s
> 30491 usecs to free memory
> test done
>
> Test run 2:
> 1073741824 bytes / 771932432 usecs = 1358 KB/s
> 31194 usecs to free memory
> 1073741824 bytes / 788739551 usecs = 1329 KB/s
> 25714 usecs to free memory
> 1073741824 bytes / 795853979 usecs = 1317 KB/s
> 33809 usecs to free memory
> 1073741824 bytes / 798019211 usecs = 1313 KB/s
> 32019 usecs to free memory
> 1073741824 bytes / 798771141 usecs = 1312 KB/s
> 31689 usecs to free memory
> 1073741824 bytes / 800384757 usecs = 1310 KB/s
> 32622 usecs to free memory
> 1073741824 bytes / 800822764 usecs = 1309 KB/s
> 1073741824 bytes / 800882227 usecs = 1309 KB/s
> 32789 usecs to free memory
> 30577 usecs to free memory
> test done
>
> Test run 3:
> 1073741824 bytes / 775202370 usecs = 1352 KB/s
> 31832 usecs to free memory
> 1073741824 bytes / 777618372 usecs = 1348 KB/s
> 30172 usecs to free memory
> 1073741824 bytes / 778180006 usecs = 1347 KB/s
> 32482 usecs to free memory
> 1073741824 bytes / 778521023 usecs = 1346 KB/s
> 30188 usecs to free memory
> 1073741824 bytes / 779207791 usecs = 1345 KB/s
> 29364 usecs to free memory
> 1073741824 bytes / 780753200 usecs = 1343 KB/s
> 29860 usecs to free memory
> 1073741824 bytes / 781078362 usecs = 1342 KB/s
> 30449 usecs to free memory
> 1073741824 bytes / 781224993 usecs = 1342 KB/s
> 19557 usecs to free memory
> test done
>
>
> After this patch:
> Test run 1:
> 1073741824 bytes / 569803736 usecs = 1840 KB/s
> 29032 usecs to free memory
> 1073741824 bytes / 573718349 usecs = 1827 KB/s
> 30399 usecs to free memory
> 1073741824 bytes / 592070142 usecs = 1771 KB/s
> 31896 usecs to free memory
> 1073741824 bytes / 593484694 usecs = 1766 KB/s
> 30650 usecs to free memory
> 1073741824 bytes / 596693866 usecs = 1757 KB/s
> 31582 usecs to free memory
> 1073741824 bytes / 597359263 usecs = 1755 KB/s
> 26436 usecs to free memory
> 1073741824 bytes / 598339187 usecs = 1752 KB/s
> 30697 usecs to free memory
> 1073741824 bytes / 598674138 usecs = 1751 KB/s
> 29791 usecs to free memory
> test done
>
> Test run 2:
> 1073741824 bytes / 578821803 usecs = 1811 KB/s
> 28433 usecs to free memory
> 1073741824 bytes / 584262760 usecs = 1794 KB/s
> 28565 usecs to free memory
> 1073741824 bytes / 586118970 usecs = 1789 KB/s
> 27365 usecs to free memory
> 1073741824 bytes / 589159154 usecs = 1779 KB/s
> 42645 usecs to free memory
> 1073741824 bytes / 593487980 usecs = 1766 KB/s
> 28684 usecs to free memory
> 1073741824 bytes / 606025290 usecs = 1730 KB/s
> 28974 usecs to free memory
> 1073741824 bytes / 607547362 usecs = 1725 KB/s
> 33221 usecs to free memory
> 1073741824 bytes / 607882511 usecs = 1724 KB/s
> 31393 usecs to free memory
> test done
>
> Test run 3:
> 1073741824 bytes / 487637856 usecs = 2150 KB/s
> 28022 usecs to free memory
> 1073741824 bytes / 491211037 usecs = 2134 KB/s
> 28229 usecs to free memory
> 1073741824 bytes / 527698561 usecs = 1987 KB/s
> 30265 usecs to free memory
> 1073741824 bytes / 531719920 usecs = 1972 KB/s
> 30373 usecs to free memory
> 1073741824 bytes / 532555758 usecs = 1968 KB/s
> 30019 usecs to free memory
> 1073741824 bytes / 532942789 usecs = 1967 KB/s
> 29354 usecs to free memory
> 1073741824 bytes / 540793872 usecs = 1938 KB/s
> 32703 usecs to free memory
> 1073741824 bytes / 541343777 usecs = 1936 KB/s
> 33428 usecs to free memory
> test done
>
> It seems to match the ~33% swapin.throughput regression reported by
> the bot, it's about ~40% faster with this patch applied. I'll add this
> test result to V2.

Oh, wow you do have the HDD number, congrates. Now we can make the
claim with numbers.
I hope you did not cripple a HDD to get that number.

Thanks.

Chris