On Fri, Aug 17, 2007 at 02:47:27PM +0800, Fengguang Wu wrote: > Matt, > > It's not easy to do direct performance comparisons between pmaps and > pagemap/kpagemap. However some close analyzes are still possible :) > > 1) code size > pmaps ~200 LOC > pagemap/kpagemap ~300 LOC > > 2) dataset size > take for example my running firefox on Intel Core 2: > VSZ 400 MB > RSS 64 MB, or 16k pages > pmaps 64 KB, wc shows 2k lines, or so much page ranges > pagemap 800 KB, could be heavily optimized by returning partial data
I take it you're in 64-bit mode? You're right, this data compresses well in many circumstances. I suspect it will suffer under memory pressure though. That will fragment the ranges in-memory and also fragment the active bits. The worst case here is huge, of course, but realistically I'd expect something like 2x-4x. But there are still the downsides I have mentioned: - you don't get page frame numbers - you can't do random access And how long does it take to pull the data out? My benchmarks show greater than 50MB/s (and that's with the version in -mm that's doing double buffering), so that 800K would take < .016s. > kpagemap 256 KB > > 3) runtime overheads > pmaps 2k lines of string processing(encode/decode) > kpagemap 16k seek()/read()s, and context switches (could be > optimized somehow by doing a PFN sort first, but > that's also non-trivial overheads) You can do anywhere between 16k small reads or 1 large read. Depends what data you're trying to get. Right now, kpagemap is fast enough that I can do realtime displays of the whole of memory in my desktop in a GUI written in Python. And Python is fairly horrible for drawing bitmaps and such. http://www.selenic.com/Screenshot-kpagemap.png > So pmaps seems to be a clear winner :) Except that it's only providing a subset of the data. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
