On Wed, Apr 04, 2007 at 04:55:32PM +0300, Dan Aloni wrote: > How about applications that perform mmap() and R/W random-access on > large *sparse* files? (e.g. a scientific app that uses a large sparse > file as a big database look-up table). As I see it, these apps would > need to keep track of what's sparse and what's not...
That's not anonymous memory if those are read page faults on _files_. I'm only talking about anonymous memory and do_anonymous_page, i.e. no file data at all. In more clear words, the only thing we're discussing here is char = malloc(1); *char. Your example _already_ allocates zeroed pagecache instead of the zero page, so your example (random access over sparse files with mmap, be it MAP_PRIVATE or MAP_SHARED no difference for reads) has never had anything to do with the zero page. If something we could optimize your example to _start_ using for the first time ever the ZERO_PAGE, it would make more sense to use it to be mapped where the lowlevel fs finds holes. ZERO_PAGE in do_anonymous_page instead doesn't make much sense to me, but it has always been there as far as I can remember. The thing is that it never hurted until the huge systems with nightmare cacheline bouncing reported heavy stalls on some testcase, which make it look like a DoS because of the ZERO_PAGE, hence now that it hurts I guess it can go. - 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/
