On Wed, Oct 22, 2008 at 04:45:24PM +0200, Miklos Szeredi wrote: > On Wed, 22 Oct 2008, Matthew Wilcox wrote: > > remap_file_pages() only hurts if you map the same page more than once > > (which is permitted, but again, I don't think anyone actually does > > that). > > This is getting very offtopic... but remap_file_pages() is just like > MAP_FIXED, that the address at which a page is mapped is determined by > the caller, not the kernel. So coherency with other, independent > mapping of the file is basically up to chance. Oh, right, I see. > Do we care? I very much hope not. Why do PA-RISC and friends care at > all about mmap coherecy? Is it real-world problem driven or just to > be safe? One reason to care is performance. If two tasks have libc mapped coherently, then the addresses will collide in the cache and they'll use the same cachelines. I don't know how much applications care about correctness with mmap -- they certainly do with sysv shm. I probably knew about some applications that broke when I was working on this code -- back in 2002. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
