Messages in this thread | | | Date | Tue, 02 Nov 2004 14:41:15 -0800 | From | "Martin J. Bligh" <> | Subject | Re: PG_zero |
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> On Tue, Nov 02, 2004 at 01:09:10PM -0800, Andrew Morton wrote: >> The cold pages are mainly intended to be the pages which will be placed >> under DMA transfers. We should never return hot pages in response for a >> request for a cold page. > > after the DMA transfer often the cpu will touch the data contents > (all the pagein/reads do that) and the previously cold page will become > hotter than the other hot pages you left in the hot list. I doubt
eh? I don't see how that matters at all. After the DMA transfer, all the cache lines will have to be invalidated in every CPUs cache anyway, so it's guaranteed to be stone-dead zero-degrees-kelvin cold. I don't see how however hot it becomes afterwards is relevant?
> there's any difference between a cache shoop or a recycle of some cache > entry because we run out of cache (in turn making some random hot cache > as cold). There's a window of time during the dma that may run faster by > allocating hot cache, but in the same window of time some other task may > as well free some hot data in turn avoiding to enter the buddy at all > and to take the zone lock.
If the DMA is to pages that are hot in the CPUs cache - it's WORSE ... we have more work to do in terms of cacheline invalidates. Mmm ... in terms of DMAs, we're talking about disk reads (ie a new page allocates) - we're both on the same page there, right?
M.
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