Il 30/05/2013 15:38, Alexey Kardashevskiy ha scritto: >>> does this problem only occur on pseries emulation? >> >> Probably not. On a PC, it would occur if you had 4K of zeros in the >> source BIOS but not in the destination BIOS. When you reboot, the BIOS >> image is wrong. >> >>> not sending zero pages is not only a performance benefit it also makes >>> overcomitted memory usable. the madv_dontneed seems to kick in >>> asynchronously >>> and memory is not available immediately. >> >> You could also scan the page for nonzero values before writing it. > > Scan where? On the source? It is there already. On the destination? Won't > just trying to read a page kill all effect from MADV_DONTNEED?
No, zero pages are handled with special copy-on-write magic by the kernel. :) So, reading works but writing doesn't. Paolo
