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TypoTypoPosted Dec 16, 2010 14:51 UTC (Thu) by Halmonster (guest, #4537)Parent article: Unmapped page cache control
Typo in the article. The patch author's name is Balbir, not Bilbir.
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Typo Posted Dec 16, 2010 15:00 UTC (Thu) by corbet (editor, #1) [Link] Given that the name was correctly spelled two times out of three, one assumes we know the correct spelling. The mistake has been fixed.As noted right above the comment box, we do prefer to receive these reports as email.
Typo Posted Dec 19, 2010 4:47 UTC (Sun) by quotemstr (subscriber, #45331) [Link]
Doesn't having the host use uncached IO to service virtualized guest IO eliminate the duplicate caching?
Obvious Answer? Posted Dec 19, 2010 6:42 UTC (Sun) by Fowl (subscriber, #65667) [Link]
Or just the disabling the cache on the guests? Thereby allowing them to all share the host's.
What am I missing?
Obvious Answer? Posted Dec 19, 2010 7:07 UTC (Sun) by quotemstr (subscriber, #45331) [Link]
It's easier and less invasive to configure a program to use unbuffered IO for a particular program's access to a particular file (a virtual disk in this case) than to disable buffering for a whole operating system, which might be actually be impossible.
Typo Posted Dec 20, 2010 11:39 UTC (Mon) by joern (subscriber, #22392) [Link]
> Doesn't having the host use uncached IO to service virtualized guest IO eliminate the duplicate caching?
It does - if only a single guest is caching the pages in question.
Interesting Posted Dec 20, 2010 14:32 UTC (Mon) by rilder (subscriber, #59804) [Link]
I don't think that is possible -- to be able to differentiate requests from the host and the guest to serve uncached to guest and cached to host -- if this is possible then it is great.
Interesting Posted Dec 20, 2010 14:39 UTC (Mon) by quotemstr (subscriber, #45331) [Link]
It's not only possible, but trivial: IO from guests goes through the hypervisor, which can use simple uncached file IO (e.g., O_DIRECT) to service these requests. Host IO goes through the normal path and uses normal buffering.
Interesting Posted Jan 3, 2011 5:17 UTC (Mon) by balbir_singh (subscriber, #34142) [Link]
Yes, it is possible, but there have been reports of large overheads in doing so. Please see the email from Chris at http://www.mail-archive.com/kvm@vger.kernel.org/msg30821.... for throughput issues.
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