From: James S. <ja...@st...> - 2003-09-21 09:12:25
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On Sun, 21 Sep 2003, Christian Jaeger wrote: > Hello > > Two++ questions: > > - Why does uml implement RAM in files in tmpfs? Why not just normal > malloc'ed memory? At least I wouldn't need to use tmpfs (which would > be a little simplification in the setup) - it'll end up in RAM or > swap anyways, so.. because if you create the vm file in /tmp or somewhere else on the disk the host will continuously write back the memory image into the disk file. Which causes a massive slowdown. This needs to happne on machines which dont have enough memory. But it also happens on some machine that do have enough memory but have a high io load on them from time to time. eg you copy a 2GB file and half of uml ends up written back to the virtual memory file and free'ed by the host. Which needs to be re-read as soon as uml is used again. I originally detected this problem where doign certin things in uml were taking ages because of the amount of io on this file. where an operation like vmstat 1 was causing a disk write every second. James |