Date: Thu, 3 Jun 2010 11:58:43 +0530 From: "C. Jayachandran" <c.jayachandran@gmail.com> To: Alan Cox <alc@imimic.com> Cc: Alan Cox <alc@cs.rice.edu>, mips@freebsd.org Subject: Re: init_pte_prot() patch Message-ID: <AANLkTikgjoYtZPOUEK2x6aWk-pXTgMlA3txFob25AL6r@mail.gmail.com> In-Reply-To: <4C0736A5.1010101@imimic.com> References: <4C0736A5.1010101@imimic.com>
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On Thu, Jun 3, 2010 at 10:29 AM, Alan Cox <alc@imimic.com> wrote: > I would appreciate it if someone would test the attached patch. (A > "buildworld" would probably suffice.) Essentially, it does two things: > > 1. The virtual memory system only cares about the contents of a page's dirty > field if that page is managed (i.e., it is pageable). And, in fact, if you > survey the calls to vm_page_dirty() in the MIPS or any other pmap, they are > generally conditioned on the mapping having been for a managed page. > > The MIPS pmap_enter() is an exception to this rule. It is unconditionally > calling vm_page_dirty() on any page mapped within the kernel address space, > managed or otherwise. In fact, it is highly unusual for pmap_enter() to be > calling vm_page_dirty() on the page being mapped, regardless of whether it > is managed. This call to vm_page_dirty() shouldn't be needed if change #2 > below is also made. The attached patch eliminates the call. > > 2. Since the virtual memory system only cares about the contents of a page's > dirty field if that page is managed, then dirty bit emulation need only be > performed on managed pages. At present, init_pte_prot() skips emulation if > the address being mapped is in the kernel. However, this is not really the > right condition to test for. There do exist some managed pages in the > kernel address space, and it is also possible through System V shared memory > to have unmanaged pages in the user address space. The attached patch bases > the emulation decision on whether the page is managed. I have added this patch to my buildworld test (make -j128 buildworld on a 8-core MIPS SoC) and it seems to be holding up. It will take a few hours to run over NFS - will update if I get anything. JC.help
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