Date: Tue, 8 Jun 2010 09:37:29 +0530 From: "C. Jayachandran" <c.jayachandran@gmail.com> To: Alan Cox <alc@cs.rice.edu> Cc: Kostik Belousov <kostikbel@gmail.com>, "Jayachandran C." <jchandra@freebsd.org>, mips@freebsd.org Subject: Re: svn commit: r208589 - head/sys/mips/mips Message-ID: <AANLkTilBxdXxXrWC1cAT0wX9ubmFrvaAdk4feG6PwDYQ@mail.gmail.com> In-Reply-To: <4C0D64B7.7060604@cs.rice.edu> References: <AANLkTimIa3jmBPMhWIOcY6DenGpZ2ZYmqwDTWspVx0-u@mail.gmail.com> <AANLkTil2gE1niUWCHnsTlQvibhxBh7QYwD0TTWo0rj5c@mail.gmail.com> <AANLkTinA2D5iTDGPbflHVzLyAZW-ZewjJkUWWL8FVskr@mail.gmail.com> <4C07E07B.9060802@cs.rice.edu> <AANLkTimjyPc_AXKP1yaJaF1BN7CAGBeNikVzcp9OCb4P@mail.gmail.com> <4C09345F.9040300@cs.rice.edu> <AANLkTinmFOZY3OlaoKStxlNIRBt2G2I4ILkQ1P0CjozG@mail.gmail.com> <4C0D2BEA.6060103@cs.rice.edu> <AANLkTikZxx_30H9geHvZYkYd0sE-wiuZljEd0PAi14ca@mail.gmail.com> <4C0D3F40.2070101@cs.rice.edu> <20100607202844.GU83316@deviant.kiev.zoral.com.ua> <4C0D64B7.7060604@cs.rice.edu>
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On Tue, Jun 8, 2010 at 2:59 AM, Alan Cox <alc@cs.rice.edu> wrote: > On 6/7/2010 3:28 PM, Kostik Belousov wrote: >> >> Selecting a random message in the thread to ask my question. >> Is the issue that page table pages should be allocated from the specific >> physical region of the memory ? If yes, doesn't i386 PAE has similar >> issue with page directory pointer table ? I see a KASSERT in i386 >> pmap that verifies that the allocated table is below 4G, but I do not >> understand how uma ensures the constraint (I suspect that it does not). >> > > For i386 PAE, the UMA backend allocator uses kmem_alloc_contig() to ensur= e > that the memory is below 4G. =A0The crucial difference between i386 PAE a= nd > MIPS is that for i386 PAE only the top-level table needs to be below a > specific address threshold. =A0Moreover, this level is allocated in a pla= ce, > pmap_pinit(), where we are allowed to sleep. Yes. I saw the PAE top level page table code and thought I could use that mechanism for allocating MIPS page table pages in the direct mapped memory. The other reference I used was pmap_alloc_zeroed_contig_pages() function in sun4v/sun4v/pmap.c which uses the vm_phys_alloc_contig() and VM_WAIT. I had also thought of using the VM_FREEPOOL_DIRECT which seemed to be for a similar purpose, but could find see any usage in the kernel. JC.
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