Re: Directories > 2GB

[Steve Lord]

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.

Steve

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