Messages in this thread | | | Date | Wed, 19 Sep 2007 17:22:46 -0400 | From | Andy Lutomirski <> | Subject | Re: A little coding style nugget of joy |
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Andi Kleen wrote: > Matt LaPlante <kernel1@cyberdogtech.com> writes: > >> Since everyone loves random statistics, here are a few gems to give you a break from your busy day: >> >> Number of lines in the 2.6.22 Linux kernel source that include one or more trailing whitespaces: 135209 >> Bytes saved by removing said whitespace: 151809 > > You don't actually save anything on disk on most file systems > (essentially everything except reiserfs on current Linux) > because all files are rounded to block size (normally 4K) > > Same in page cache.
This is a terrible assumption in general (i.e. if filesize % blocksize is close to uniformly distributed). If you remove one byte and the data is stored with blocksize B, then you either save zero bytes with probability 1-1/B or you save B bytes with probability 1/B. The expected number of bytes saved is B*1/B=1. Since expectation is linear, if you remove x bytes, the expected number of bytes saved is x (even if there is more than one byte removed per file).
In my tree, about half of the files have size >= 4k, so the assumption is probably not _that_ far off the mark.
Alternatively, there are an average of about 16 bytes removed per file, and there are 11 which are <= 16 bytes short of a 4k boundary, so it's not at all unreasonable that we'd save 40-50k.
> > And in tar files bzip2/gzip is very good at compacting them.
That's true.
--Andy - 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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