Re: [Fwd: Page allocator doubt]

Marcelo Tosatti
2004-11-11T21:21:01Z

On Thu, Nov 11, 2004 at 06:22:51PM -0200, Luciano A. Stertz wrote:
> Dave Hansen wrote:
> >On Thu, 2004-11-11 at 11:27, Luciano A. Stertz wrote:
> >
> >> But... are they allocated to me, even with page_count zeroed? Do I
> >> need to do get_page on the them? Sorry if it's a too lame question, but I
> >>still didn't understand and found no place to read about this.
> >
> >
> >Do you see anywhere in the page allocator where it does a loop like
> >yours?
> >
> > for (i = 1; i< 1<<order; i++)
> > get_page(page + i);
> Actually this loop isn't mine. It's part of the page allocator, but
> it's only executed on systems without a MMU.
>
> >When you do a multi-order allocation, the first page represents the
> >whole group and they're treated as a whole. As you've noticed, breaking
> >them up requires a little work.
> >
> >Why don't you post all of the code that you're using so that we can tell
> >what you're doing? There might be a better way. Drivers probably
> >shouldn't be putting stuff in the page cache all by themselves.
> Unhappily I can't post any code yet, but I'll try to give an insight
> of what we're trying to do.
> It's not a driver. We're doing an implementation to allow the kernel
> to execute compressed files, decompressing pages on demand.
> These files will usually be compressed in small blocks, typically
> 4kb. But if they got compressed in blocks bigger then a page (say 8kb
> blocks on a 4kb page system), the kernel will have more than one
> decompressed page each time a block have to be decompressed; and I'd like
> to add them both to the page cache.
> So, seems I would have to break multi-order allocated pages. Is this
> possible / viable? If not, maybe I'll have to work only with small
> blocks, but I wouldn't like to...

Why do you need the pages to be physically contiguous?

I dont see any reason for that requirement - you can use discontiguous physical
pages which are virtually contiguous (so your decompression code wont need to
care about non adjacent pieces of memory).