On Mon, Sep 29, 2014 at 9:55 PM, Daniel Micay <danielmicay@xxxxxxxxx> wrote: > This introduces the MREMAP_RETAIN flag for preserving the source mapping > when MREMAP_MAYMOVE moves the pages to a new destination. Accesses to > the source location will fault and cause fresh pages to be mapped in. > > For consistency, the old_len >= new_len case could decommit the pages > instead of unmapping. However, userspace can accomplish the same thing > via madvise and a coherent definition of the flag is possible without > the extra complexity. IMO this needs very clear documentation of exactly what it does. Does it preserve the contents of the source pages? (If so, why? Aren't you wasting a bunch of time on page faults and possibly unnecessary COWs?) Does it work on file mappings? Can it extend file mappings while it moves them? If you MREMAP_RETAIN a partially COWed private mapping, what happens? Does it work on special mappings? If so, please prevent it from doing so. mremapping x86's vdso is a thing, and duplicating x86's vdso should not become a thing, because x86_32 in particular will become extremely confused. --Andy -- 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>