Messages in this thread | | | From | "" <> | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable | Date | Sun, 6 Jan 2002 13:51:58 -0200 |
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On 5 January 2002 10:59, M. Edward (Ed) Borasky wrote:
> OK, here's some pseduo-code for a real-world test case. I haven't had a > chance to code it up, but I'm guessing I know what it's going to do. I'd > *love* to be proved wrong :). > > # build and boot a kernel with "Magic SysRq" turned on > # echo 1 > /proc/sys/kernel/sysrq > # fire up "nice --19 top" as "root" > # read "MemTotal" from /proc/meminfo > > # now start the next two jobs concurrently > > # write a disk file with "MemTotal" data or more in it
Like dd if=/dev/zero of=/tmp/file bs=... count=... ?
> # perform a 2D in-place FFT of total size at least "MemTotal/2" but less > # than "MemTotal"
I'm willing to try. What program can I use for FFT?
> What's worse is if the page cache gets so big that the FFT has to start > swapping. For those who aren't familiar with 2D FFTs, they take two > passes over the data. The first pass will be unit strides -- sequential > addresses. But the second pass will be large strides -- a power of two. > That second pass is going to be brutal if every page it hits has to be > swapped in!
Can you describe FFT memory access pattern in more detail? I'd like to write a simple testcase with similar 'bad' pattern. -- vda - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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