On Monday 15 October 2007 10:57, Jeremy Fitzhardinge wrote:Yeah, it would be possible. The easiest way would just be to shoot down all lazy vmaps (because you're doing the global IPIs anyway, which are the expensive thing, at which point you may as well purge the rest of your lazy mappings). If it is sufficiently rare, then it could be the simplest thing to do. OK. OK, I see. Because even though it is technically safe where we are using it (because nothing writes through the mappings after the page is freed), a corrupted guest could use the same window to do bad things with the pagetables? vmap is slightly harder than kmap in some respects. However it would be really nice to get vmap fast and general enough to completely replace all the kmap crud -- that's one goal, but the first thing I'm doing is to concentrate on just vmap to work out how to make it as fast as possible. For Xen -- shouldn't be a big deal. We can have a single Linux mm API to call, and we can do the right thing WRT vmap/kamp. I should try to merge my current lazy vmap patches which replace the XFS stuff, so we can implement such an API and fix your XFS issue? That's not going to happen for at least a cycle or two though, so in the meantime maybe an ifdef for that XFS vmap batching code would help? -
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| Peter Zijlstra | Re: + mm-balance_dirty_pages-reduce-calls-to-global_page_state-to-reduce-c ache-re... |
