Comment 44 for bug 727064

On Mon, Aug 12, 2013 at 05:19:54PM +0000, tudorb at gmail dot com wrote:
> --- Comment #28 from Tudor Bosman <tudorb at gmail dot com> ---
> FYI, this bug has bitten me in a different way: memcpy() copying backwards
> defeats the MADV_SEQUENTIAL flag to madvise(). A trivial file copier
> implementation (mmap source, mmap destination, set MADV_SEQUENTIAL, memcpy from
> source to destination) would perform much worse on machines that support SSSE3
> than on machines that don't because of this bug.
>
Wait, do you have overlapping source and destination areas? If so then a
backward copy is necessary.

Or is backward copy called for not overlapping areas?
I have a patch that could call backward copy only if src-n < dest < src+n holds.

> (Before anyone tells me that I should copy files using read() and write(), my
> actual usage pattern was more complex, but the details are irrelevant.)
>
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