> On Thu, Jan 14, 2010 at 04:02:42PM +0900, KOSAKI Motohiro wrote: > > > On Thu, Jan 14, 2010 at 09:31:03AM +0900, KOSAKI Motohiro wrote: > > > > > If application does mlockall(MCL_FUTURE) it is no longer possible to mmap > > > > > file bigger than main memory or allocate big area of anonymous memory > > > > > in a thread safe manner. Sometimes it is desirable to lock everything > > > > > related to program execution into memory, but still be able to mmap > > > > > big file or allocate huge amount of memory and allow OS to swap them on > > > > > demand. MAP_UNLOCKED allows to do that. > > > > > > > > > > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx> > > > > > --- > > > > > > > > > > I get reports that people find this useful, so resending. > > > > > > > > This description is still wrong. It doesn't describe why this patch is useful. > > > > > > > I think the text above describes the feature it adds and its use > > > case quite well. Can you elaborate what is missing in your opinion, > > > or suggest alternative text please? > > > > My point is, introducing mmap new flags need strong and clearly use-case. > > All patch should have good benefit/cost balance. the code can describe the cost, > > but the benefit can be only explained by the patch description. > > > > I don't think this poor description explained bit benefit rather than cost. > > you should explain why this patch is useful and not just pretty toy. > > > The benefit is that with this patch I can lock all of my application in > memory except some very big memory areas. My use case is that I want to > run virtual machine in such a way that everything related to machine > emulator is locked into the memory, but guest address space can be > swapped out at will. Guest address space is so huge that it is not > possible to allocated it locked and then unlock. I was very surprised > that current Linux API has no way to do it hence this patch. It may look > like a pretty toy to you until some day you need this and has no way to > do it. Hmm.. Your answer didn't match I wanted. few additional questions. - Why don't you change your application? It seems natural way than kernel change. - Why do you want your virtual machine have mlockall? AFAIK, current majority virtual machine doesn't. - If this feature added, average distro user can get any benefit? I mean, many application developrs want to add their specific feature into kernel. but if we allow it unlimitedly, major syscall become the trushbox of pretty toy feature soon. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
