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Date: Thu, 24 Apr 2008 21:27:19 +0200 From: Andi Kleen <andi@...stfloor.org> To: Timur Tabi <timur@...escale.com> Cc: lkml <linux-kernel@...r.kernel.org> Subject: Re: Calling free_pages on part of the memory returned by get_free_pages? Timur Tabi <timur@...escale.com> writes: > According to LDD3, if I call get_free_pages() to allocate X bytes, I have to > free all of those pages with free_pages(). The VM internals are a little bit > over my head, but I looked at the code and I didn't see why that is a requirement. > > For example, let's say I want to allocated 6MB of physically-contiguous memory. > If I call x = get_free_pages(11) to get 8MB. What happens if I then do > "free_pages(x + 6 * 1024 * 1024, 9)"? > > I remember doing this on the 2.4 kernel, and it never gave me any problems. It is ok, as long as you don't use compound pages (__GFP_COMP) and call split_page() to fix up the reference counts. Also you do this to save memory right? The large system hash code does it too and I used to do it in some 2.4 change with an alloc_pages_exact() which never made it into 2.6. If it's reasonably common we should re-add alloc/get_pages_exact() helper to make this pattern clear and easier to use. -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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