Messages in this thread |  | | Date | Fri, 05 Oct 2001 15:32:18 +0200 | From | Bernd Harries <> | Subject | Re: __get_free_pages(): is the MEM really mine? |
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Hugh Dickins wrote:
> I don't > know whether you're following the mmap-makes-all-pages-present > model (using remap_page_range), or the fault-page-by-page model > (supplying your own nopage function).
The nopage method. In Alessandro Rubini's book (p.391) I read, that I can't use remap_page_range() on pages optained by get_free_page().
> But either way it sounds like > you bump each page count by 1 when you map it in, and then when > it's unmapped the count goes down to 0 on all the later > order-0-pages,
exactly that happens in the version I use on minor 26 today.
> so they get freed before you're done with them.
Hmm, the only thing that happens to them after munmap() is free_pages(). I don't access the pages anymore. But maybe some code in free_pages does? Or decrements count to -1?
> Either you should force page count 1 on each of the > order-0-pages before you mmap them in
Yes, I do that in the version used in minor 27 today right after the allocation.
> (and raise count to 2);
by get_page(), right?
> or you should set > the Reserved bit on each them, and clear it before freeing > (see use of mem_map_reserve and mem_map_unreserve in various > drivers/sound > sources using remap_page_range; there's also a couple of > examples of the nopage method down there too).
Ok, thanks a lot. So it's definitely insufficient how my minor 26 version handles the pages, right? If so, that's a statement I can live with.
And it was never ment that I could simply mmap the upper pages to userspace directly, without 'touching' each page, was it?
Ciao, -- Bernd Harries
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