Messages in this thread | | | Date | Sat, 8 Dec 2001 03:02:36 +0100 | From | Jens Axboe <> | Subject | Re: highmem question |
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On Fri, Dec 07 2001, H. Peter Anvin wrote: > Jens Axboe wrote: > > > On Fri, Dec 07 2001, Marvin Justice wrote: > > > >>>There is no way of fixing it. > >>> > >>All I know is that a streaming io app I was playing with showed a drastic > >>performance hit when the kernel was compiled with CONFIG_HIGHMEM. On W2K we > >>saw no slowdown with 2 or even 4GB of RAM so I think solutions must exist. > >> > > > > That's because of highmem page bouncing when doing I/O. There is indeed > > a solution for this -- 2.5 or 2.4 + block-highmem-all patches will > > happily do I/O directly to any page in your system as long as your > > hardware supports it. I'm sure we're beating w2k with that enabled :-) > > > > > I didn't realize we were doing page bouncing for I/O in the 1-4 GB range. > Yes, this would be an issue.
All due to the "old" block stuff requiring a virtual mapping traditionally for doing I/O. Ugh. So yes, we are bouncing _any_ highmem page.
-- Jens Axboe
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