Date: Thu, 3 Jun 2010 10:20:43 +0530 From: "C. Jayachandran" <c.jayachandran@gmail.com> To: Alan Cox <alc@cs.rice.edu> Cc: "Jayachandran C." <jchandra@freebsd.org>, svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Randall Stewart <rrs@lakerest.net> Subject: Re: svn commit: r208589 - head/sys/mips/mips Message-ID: <AANLkTimIa3jmBPMhWIOcY6DenGpZ2ZYmqwDTWspVx0-u@mail.gmail.com> In-Reply-To: <4C0731A5.7090301@cs.rice.edu> References: <201005271005.o4RA5eVu032269@svn.freebsd.org> <4C058145.3000707@cs.rice.edu> <AANLkTil955Ek-a3tek4Ony9NqrK5l2j7lNA4baRVPBzb@mail.gmail.com> <4C05F9BC.40409@cs.rice.edu> <AANLkTikdnvXsTwm8onl3MZPQmVfV-2GovB9--KMNnMgC@mail.gmail.com> <4C0731A5.7090301@cs.rice.edu>
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--000e0cd1aa3efa00ac048818f237 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Thu, Jun 3, 2010 at 10:07 AM, Alan Cox <alc@cs.rice.edu> wrote: > C. Jayachandran wrote: >> >> On Wed, Jun 2, 2010 at 11:57 AM, Alan Cox <alc@cs.rice.edu> wrote: >> >>> >>> C. Jayachandran wrote: >>> >>>> >>>> On Wed, Jun 2, 2010 at 3:23 AM, Alan Cox <alc@cs.rice.edu> wrote: >>>> >>>> >>>>> >>>>> On 5/27/2010 5:05 AM, Jayachandran C. wrote: >>>>> >>>>> >>>>>> >>>>>> Author: jchandra >>>>>> Date: Thu May 27 10:05:40 2010 >>>>>> New Revision: 208589 >>>>>> URL: http://svn.freebsd.org/changeset/base/208589 >>>>>> >>>>>> Log: >>>>>> =A0Call VM_WAIT in pmap_ptpgzone_allocf() if =A0M_WAITOK is set. >>>>>> =A0Removed unused variable. >>>>>> >>>>>> =A0Approved by: rrs (mentor) >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>>> I'm afraid that this will work some of the time, but not all of the >>>>> time. >>>>> =A0Specifically, there is no guarantee that any of the available free= (or >>>>> cached) pages after the VM_WAIT will fall within the range of suitabl= e >>>>> physical addresses. =A0Moreover, and perhaps most worrisome, is that = this >>>>> function could do a lot of spinning. =A0Every time this function slee= ps >>>>> and >>>>> a >>>>> single page is freed (or cached) by someone else, this function will = be >>>>> reawakened. =A0With a little bad luck, you could spin indefinitely. >>>>> >>>>> For essentially this reason, contigmalloc(), kmem_alloc_contig(), and >>>>> kmem_alloc_attr() don't use VM_WAIT, but instead a function called >>>>> vm_contig_grow_cache(). >>>>> >>>>> >>>> >>>> I had seen the vm_contig_grow_cache() usage, but could not use it as >>>> it was defined as a static function. >>>> >>>> I did not want to use contigmalloc()/kmem_alloc_contig() either, >>>> because the pages in that memory region are already direct mapped and >>>> setting up another mapping is not necessary. The overall idea is to >>>> allocate pages in the direct mapped region for the page table entries >>>> so that we don't take a TLB exception while accessing page tables >>>> (which is costly as MIPS has a software TLB exception handler). >>>> >>>> Can you suggest the right way to do this? I will make the changes and >>>> send a patch for approval. >>>> >>>> >>> >>> I would encourage you to make vm_contig_grow_cache() an extern function >>> and >>> use it. =A0(vm/vm_pageout.h is probably the best place for the function >>> prototype.) >>> >> >> I'll create a patch for this and related changes in mips/mips/pmap.c >> >> > > Great. =A0Thanks! > >>> If you're interested in taking this a small step further, it would make >>> sense to add two parameters to vm_contig_grow_cache() and >>> vm_contig_launder(): a "low" and a "high" physical address. >>> =A0vm_contig_launder() could then skip pages that are outside the desir= ed >>> range. >>> >> >> I am looking at this now, =A0part of the logic which >> vm_phys_alloc_contig() uses to check pages address should work here. >> Will send out changes for this, if it works out. >> >> > > I suspect that you'll just need to add two or three lines to > vm_contig_launder(). =A0If something doesn't make sense, just e-mail me. The current changes I have is attached - still testing it. 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