Messages in this thread | | | Date | Sat, 26 Feb 2011 15:37:30 +0100 | From | Tejun Heo <> | Subject | [RFC] Reverting NUMA-affine page table allocation |
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Hello,
I've been looking through NUMA-affine page table allocation code and the proposed changes, and there currently are the a couple of problems.
1. Holes or misaligned nodes will force use of smaller sized mappings. Patches to fix the problem have been posted by Yinghai[1].
2. find_early_table_space() always calculates the amount of the needed space from 0 to the specified @end. As nodes are registered, each node would try to allocate accumulative amount of space for page table. This probably wouldn't cause any actual problem (may affect emulated configurations a bit tho).
IMHO, it would be better to avoid adding fixes for #1 and #2 at this stage as we're very close to the next merge window and this is (somewhat unnecessarily) delicate piece of code. Also, I do think that the NUMA affine page table allocation is generally overdone given its limited usefulness when 1GiB mapping is available.
I'd like to revert NUMA-affine page table allocation for now and come back to it in the next devel cycle. Thanks to the memblock top-down change, the RED-PEN condition (page table ending up in DMA memory) doesn't exist with or without NUMA affine allocation and the only downside of reverting would be page tables allocated in foreign nodes on machines which don't support 1GiB mapping.
What do you think?
Thanks.
-- tejun
[1] http://thread.gmane.org/gmane.linux.kernel/1104672
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