Messages in this thread | | | Date | Fri, 17 Mar 2006 08:28:07 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH 10 of 20] ipath - support for userspace apps using core driver |
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On Fri, 17 Mar 2006, Bryan O'Sullivan wrote: > > Hmm. Which of the implementations that you've seen will return > something not backed by a struct page? On the half dozen arches I've > looked at (i386/x86_64, powerpc, sparc64, ia64, mips), every one uses > either kmalloc, __get_free_pages, or __alloc_pages at some point, and I > think they all have struct pages behind them.
kmalloc may be backed by a "struct page", but the point is that it does not honor the page _count_, and as such it is totally unsuitable for any VM usage.
The VM relies on the page count very fundamentally, so by doing a "get_page()" you'll tell every other user that you have a reference to a page, and it won't be free'd until all references are gone. In contrast, if you do a "get_page()" on something that has been allocated with kmalloc(), the slab code will totally ignore it, and happily re-allocate it to something else once the _original_ allocator free's it.
So kmalloc() really isn't appropriate.
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