On Wed, Oct 11, 2006 at 11:49:10AM -0500, Steve Lord wrote:
> David Chinner wrote:
> >On Tue, Oct 10, 2006 at 10:19:04AM +0100, Christoph Hellwig wrote:
> >>On Mon, Oct 09, 2006 at 09:15:28PM -0500, Steve Lord wrote:
> >>>Hi Dave,
> >>>
> >>>My recollection is that it used to default to on, it was disabled
> >>>because it needs to map the buffer into a single contiguous chunk
> >>>of kernel memory. This was placing a lot of pressure on the memory
> >>>remapping code, so we made it not default to on as reworking the
> >>>code to deal with non contig memory was looking like a major
> >>>effort.
> >>Exactly. The code works but tends to go OOM pretty fast at least
> >>when the dir blocksize code is bigger than the page size. I should
> >>give the code a spin on my ppc box with 64k pages if it works better
> >>there.
> >
> >The pagebuf code doesn't use high-order allocations anymore; it uses
> >scatter lists and remapping to allow physically discontiguous pages
> >in a multi-page buffer. That is, the pages are sourced via
> >find_or_create_page() from the address space of the backing device,
> >and then mapped via vmap() to provide a virtually contigous mapping
> >of the multi-page buffer.
> >
> >So I don't think this problem exists anymore...
>
> I was not referring to high order allocations here, but the overhead
> of doing address space remapping every time a directory is accessed.
Ah - ok. contig -> non-contig and OOM is usually discussed in the
context of higher order allocations failing. FWIW, I've not noticed
any extra overhead - the CPU usage seems to grow roughly linearly
with the increase in directory operations done as a result of
higher throughput for the same number of I/Os. I'll have a look at
the Vm stats, though, next time I run a comparison to see how bad
this is.
Thanks for the clarification, Steve.
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
