On 3/19/24 09:21, Thomas Gleixner wrote:
On Mon, Mar 18 2024 at 20:13, Arnd Bergmann wrote:FWIW, I did some experiments a few weeks ago on 32-bit ARM, using a fairly minimal kernel in a virtual machine, and checking the runtime memory consumption rather than compile-time. In a kvm guest with 32MiB RAM, I saw a difference of multiple megabytes in memory usage: Linux testvm 6.8.0-rc4-00410-gc02197fc9076-dirty #1 SMP PREEMPT armv7l root@testvm:~# free total used free shared buff/cache available Mem: 26932 14956 1732 52 12800 11976 Swap: 16360 3632 12728 Linux testvm 6.8.0-rc4-00410-gc02197fc9076-dirty #2 PREEMPT armv7l root@testvm:~# free total used free shared buff/cache available Mem: 26932 13744 5648 32 10092 13188 Swap: 16360 3880 12480 There is a little difference between runs, but this does seem significant enough to keep it. The SMP build was with CONFIG_NR_CPUS=2 (the smallest supported compile-time number), but running on a single-CPU qemu instance.With a SMP=y, NR_CPUS=1 build on x86 64bit I get: total used free shared buff/cache available Mem: 32882056 498068 32590580 4884 128884 32383988 Swap: 998396 0 998396 Same config just SMP=n: total used free shared buff/cache available Mem: 32885804 461704 32635284 4876 119480 32424100 Swap: 998396 0 998396 So the delta for available is ~40 MiB. But if I look at it with init=/bin/sh on the command line then the delta is significantly different: With a SMP=y, NR_CPUS=1 build on x86 64bit I get: total used free shared buff/cache available Mem: 32883680 324120 32822728 216 10864 32559560 Swap: 0 0 0 Same config just SMP=n: total used free shared buff/cache available Mem: 32885804 326876 32821972 216 11100 32558928 Swap: 0 0 0 Delta available = 632 KiB I haven't had the time to stare at that in detail, but comparing /proc/meminfo for the full boot case above does not immediately give me a hint. It's confusing at best...
That makes me wonder if the number is affected by the total memory size. How about a system with 1GB of memory or less ? Guenter
