C. Jayachandran wrote:
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
Great. Thanks!
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.
I suspect that you'll just need to add two or three lines to
vm_contig_launder(). If something doesn't make sense, just e-mail me.
Regards,
Alan
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