Date: Sat, 13 Jul 2002 09:36:50 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: David Schultz <dschultz@uclink.Berkeley.EDU> Cc: Peter Wemm <peter@wemm.org>, Sean Kelly <smkelly@zombie.org>, hackers@FreeBSD.ORG Subject: Re: swapoff? Message-ID: <200207131636.g6DGaoqh081285@apollo.backplane.com> References: <20020713071911.GA1558@HAL9000.wox.org> <20020713073404.9869A3811@overcee.wemm.org> <20020713115746.GA2162@HAL9000.wox.org>
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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.
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.
-Matt
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