Date: Sat, 13 Jul 2002 14:00:35 -0700 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Peter Wemm <peter@wemm.org>, Sean Kelly <smkelly@zombie.org>, hackers@FreeBSD.ORG Subject: Re: swapoff? Message-ID: <20020713210035.GA363@HAL9000.wox.org> In-Reply-To: <200207131636.g6DGaoqh081285@apollo.backplane.com> References: <20020713071911.GA1558@HAL9000.wox.org> <20020713073404.9869A3811@overcee.wemm.org> <20020713115746.GA2162@HAL9000.wox.org> <200207131636.g6DGaoqh081285@apollo.backplane.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Thus spake Matthew Dillon <dillon@apollo.backplane.com>: > We are not going to be doing any sort of weighting. It's an idea whos > time has come... and gone again. It might have been useful 8 years ago > but it is not useful today. > > Also, please note that it is not possible to reverse-lookup a swap bitmap > block and get the VM object / page number. The OBJT_SWAP VM objects have > to be scanned to get the swap bitmap blocks. Nor does it make much sense > to try to 'record' the blocks somewhere, there could be hundreds of > thousands of blocks and memory is not normally a luxury in this situation. I'm aware of that. That's why swapoff is a harder project; it requires working at more levels of abstraction, not all of which I fully understand yet. At least most of the VM stuff is well-documented now. ;-) > All you need to do is prevent new blocks from being allocated from the > old swap device. Since the radix tree bitmap code cannot make a > distinction between devices the easiest way to do this is to simply > allocate all the free bits associated with the device (which you can do), > and prevent any existing allocated blocks from being freed from the > bitmap (which is a simple calculation) ... and of course mark the page > dirty again since its backing store is being ripped out from under it. This makes sense. I was originally thinking of marking the device as off-limits to new allocations, but I realize now why that would not work. As long as the logical swap blocks that correspond to the device are still fair game for the swap pager, swapdev_strategy will still have to swap out to the device. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20020713210035.GA363>