On Wed, Jun 2, 2010 at 11:57 AM, Alan Cox <a...@cs.rice.edu> wrote: > C. Jayachandran wrote: >> >> On Wed, Jun 2, 2010 at 3:23 AM, Alan Cox <a...@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: >>>> Call VM_WAIT in pmap_ptpgzone_allocf() if M_WAITOK is set. >>>> Removed unused variable. >>>> >>>> Approved by: rrs (mentor) >>>> >>>> >>>> >>> >>> I'm afraid that this will work some of the time, but not all of the time. >>> Specifically, there is no guarantee that any of the available free (or >>> cached) pages after the VM_WAIT will fall within the range of suitable >>> physical addresses. Moreover, and perhaps most worrisome, is that this >>> function could do a lot of spinning. Every time this function sleeps and >>> a >>> single page is freed (or cached) by someone else, this function will be >>> reawakened. With 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. (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 > 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. > vm_contig_launder() could then skip pages that are outside the desired > range. I am looking at this now, part 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. Thanks, JC. _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
