On Wednesday 07 March 2007 10:44, Bill Irwin wrote: > On Wed, Mar 07, 2007 at 10:28:21AM +0100, Nick Piggin wrote: > > Depending on whether anyone wants it, and what features they want, we > > could emulate the old syscall, and make a new restricted one which is > > much less intrusive. > > For example, if we can operate only on MAP_ANONYMOUS memory and specify > > that nonlinear mappings effectively mlock the pages, then we can get > > rid of all the objrmap and unmap_mapping_range handling, forget about > > the writeout and msync problems... > > Anonymous-only would make it a doorstop for Oracle, since its entire > motive for using it is to window into objects larger than user virtual > address spaces (this likely also applies to UML, though they should > really chime in to confirm).
We need it for shared file mappings (for tmpfs only). Our scenario is: RAM is implemented through a shared mapped file, kept on tmpfs (except by dumb users); various processes share an fd for this file (it's opened and immediately deleted). We maintain page tables in x86 style, and TLB flush is implemented through mmap()/munmap()/mprotect(). Having a VMA per each 4K is not the intended VMA usage: for instance, the default /proc/sys/vm/max_map_count (64K) is saturated by a UML process with 64K * 4K = 256M of resident memory. > Restrictions to tmpfs and/or ramfs would > likely be liveable, though I suspect some things might want to do it to > shm segments (I'll ask about that one). > There's definitely no need for a > persistent backing store for the object to be remapped in Oracle's case, > in any event. It's largely the in-core destination and source of IO, not > something saved on-disk itself. > > > -- wli -- Inform me of my mistakes, so I can add them to my list! Paolo Giarrusso, aka Blaisorblade http://www.user-mode-linux.org/~blaisorblade Chiacchiera con i tuoi amici in tempo reale! http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
