Date: Sat, 29 Apr 2006 10:36:41 -0700 From: Nate Lawson <nate@root.org> To: Peter Wemm <peter@wemm.org> Cc: src-committers@freebsd.org, cvs-all@freebsd.org, cvs-src@freebsd.org Subject: Re: cvs commit: src/sys/i386/i386 pmap.c Message-ID: <4453A429.5080406@root.org> In-Reply-To: <200604291021.12379.peter@wemm.org> References: <200604281905.k3SJ59MZ008806@repoman.freebsd.org> <20060429024850.GB997@turion.vk2pj.dyndns.org> <4452FB64.7030308@root.org> <200604291021.12379.peter@wemm.org>
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Peter Wemm wrote: > Stephan realized that the kernel already allocates one PTE per virtual > page. Although it normally holds physical addresses plus attributes, > as long as we don't set PG_V, then there are 31 other bits that we > could use for data storage. We could put virtual addresses in there so > long as we didn't set PG_V, and abuse that to have a singly linked > freelist threaded through the PTEs. It turned out even easier though. > As long as the virtual addresses are page aligned, we neatly avoid all > the PG_* mode bits as well. ... because you can shift by the page size, saving 12 bits. But are there any problems with 2 MB pages? Great ideas, both you and ups@. You know, you can store 2 pointers there with XOR. ;-) -- Nate
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