Messages in this thread |  | | | Date | Tue, 1 Mar 2011 09:29:15 +0100 | | From | Tejun Heo <> | | Subject | Re: questions about init_memory_mapping_high() |
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Hey,
(sorry about the earlier empty reply, fat finger on my phone)
On Mon, Feb 28, 2011 at 10:14:44AM -0800, H. Peter Anvin wrote: > > 1. The only rationale given in the commit description is that a > > RED-PEN is killed, which was the following. > > > > /* > > * RED-PEN putting page tables only on node 0 could > > * cause a hotspot and fill up ZONE_DMA. The page tables > > * need roughly 0.5KB per GB. > > */ > > > > This already wasn't true with top-down memblock allocation. > > > > The 0.5KB per GiB comment is for 32bit w/ 3 level mapping. On > > 64bit, it's ~4KiB per GiB when using 2MiB mappings and, well, very > > small per GiB if 1GiB mapping is used. Even with 2MiB mapping, > > 1TiB mapping would only be 4MiB. Under ZONE_DMA, this could be > > problematic but with top-down this can't be a problem in any > > realistic way in foreseeable future. > > > > It's true on 64 bits too when PAE is not available (e.g. with Xen.)
Hmm... I don't follow. Can you elaborate? If PAE is not available for whatever reason, the physical memory is limited to 4GiB but I don't follow what that has to do with the above.
Thanks.
-- tejun
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