On 10/07/2013 05:13 PM, Minchan Kim wrote: > Hello Peter, > > On Mon, Oct 07, 2013 at 04:59:40PM -0700, H. Peter Anvin wrote: >> On 10/07/2013 04:54 PM, John Stultz wrote: >>>> And wouldn't this apply to MADV_DONTNEED just as well? Perhaps what we >>>> should do is an enhanced madvise() call? >>> Well, I think MADV_DONTNEED doesn't *have* do to anything at all. Its >>> advisory after all. So it may immediately wipe out any data, but it may not. >>> >>> Those advisory semantics work fine w/ VRANGE_VOLATILE. However, >>> VRANGE_NONVOLATILE is not quite advisory, its telling the system that it >>> requires the memory at the specified range to not be volatile, and we >>> need to correctly inform userland how much was changed and if any of the >>> memory we did change to non-volatile was purged since being set volatile. >>> >>> In that way it is sort of different from madvise. Some sort of an >>> madvise2 could be done, but then the extra purge state argument would be >>> oddly defined for any other mode. >>> >>> Is your main concern here just wanting to have a zero-fill mode with >>> volatile ranges? Or do you really want to squeeze this in to the madvise >>> call interface? >> The point is that MADV_DONTNEED is very similar in that sense, >> especially if allowed to be lazy. It makes a lot of sense to permit >> both scrubbing modes orthogonally. >> >> The point you're making has to do with withdrawal of permission to flush >> on demand, which is a result of having the lazy mode (ongoing >> permission) and having to be able to withdraw such permission. > I'm sorry I could not understand what you wanted to say. > Could you elaborate a bit? My understanding of his point is that VRANGE_VOLATILE is like a lazy MADV_DONTNEED (with sigbus, rather then zero fill on fault), suggests that we should find a way to have VRANGE_VOLATILE be something like MADV_DONTNEED|MADV_LAZY|MADV_SIGBUS_FAULT, instead of adding a new syscall. This would provide more options, since one could instead just do MADV_DONTNEED|MADV_LAZY if they wanted zero-fill faults. And indeed, for the VRANGE_VOLATILE case, we could do something like that, but the unresolved problem I see is that that we still need to handle the VRANGE_NONVOLATILE case, and the madvise() interface doesn't seem to accomodate the needed semantics well. thanks -john -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>