On Tuesday 18 September 2007 02:58, Peter Zijlstra wrote: > On Mon, 17 Sep 2007 22:11:25 -0700 Daniel Phillips wrote: > > > I've been using Avi Kivity's patch from some time ago: > > > http://lkml.org/lkml/2004/7/26/68 > > > > Yes. Ddsnap includes a bit of code almost identical to that, which > > we wrote independently. Seems wild and crazy at first blush, > > doesn't it? But this approach has proved robust in practice, and is > > to my mind, obviously correct. > > I'm so not liking this :-(
Why don't you share your specific concerns? > Can't we just run the user-space part as mlockall and extend netlink > to work with PF_MEMALLOC where needed? > > I did something like that for iSCSI. Not sure what you mean by extend netlink. We do run the user daemons under mlockall of course, this is one of the rules I stated earlier for daemons running in the block IO path. The problem is, if this userspace daemon allocates even one page, for example in sys_open, it can deadlock. Running the daemon in PF_MEMALLOC mode fixes this problem robustly, provided that the necessary audit of memory allocation patterns and library dependencies has been done. I suppose you are worried that the userspace code could unexpectedly allocate a large amount of memory and exhaust the entire PF_MEMALLOC reserve? Kernel code could do that too. This userspace code just needs to be checked carefully. Perhaps we could come up with a kernel debugging option to verify that a task does in fact stay within some bounded number of page allocs while in PF_MEMALLOC mode. Regards, Daniel - 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/
