Messages in this thread | | | Date | Sun, 4 Apr 2004 01:27:17 +0200 | From | Andrea Arcangeli <> | Subject | Re: [RFC][PATCH 1/3] radix priority search tree - objrmap complexity fix |
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On Sat, Apr 03, 2004 at 12:02:27PM -0800, Andrew Morton wrote: > It might be better to switch over to address masking in get_user_pages() > and just dump all the compound page logic. I don't immediately see how the
I'm all for it, this is how the 2.4 get_user_pages deals with bigpages too, I've never enjoyed the compound thing.
> get_user_pages() caller can subsequently do put_page() against the correct > pageframe, but I assume you worked that out?
see this patch:
http://www.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23aa2/9910_shm-largepage-18.gz
it's a two liner fix in follow_page:
@@ -439,6 +457,8 @@ static struct page * follow_page(struct pmd = pmd_offset(pgd, address); if (pmd_none(*pmd)) goto out; + if (pmd_bigpage(*pmd)) + return __pmd_page(*pmd) + (address & BIGPAGE_MASK) / PAGE_SIZE;
the BIGPAGE_MASK will never expose anything but the page->private to the get_user_pages code, and handle_mm_fault takes care of doing the page faults properly using larepages and pmds if the vma is marked VM_BIGPAGE.
rawio on largepages has been a must-have feature (especially on >=32G) for more than one year, definitely no need of compound slowdown for that.
Still I would like to understand what's wrong in Christoph's ppc machine before dumping the whole compound thing. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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