Whoops sorry, I just realized I sent a stale patch. The correct patch is here: https://github.com/CAFxX/tar/commit/8b3ccb099c6ddf9f03d12d1f7c433c7927b964d5 <https://github.com/CAFxX/tar/commit/8b3ccb099c6ddf9f03d12d1f7c433c7927b964d5>
As Mark correctly points out, ORing the constants always yields EINVAL. > On Mar 30, 2017, at 3:01 AM, Mark <ma...@clara.co.uk> wrote: > > On Wed, March 29, 2017 10:01, Joerg Schilling wrote: >> Paul Eggert <egg...@cs.ucla.edu> wrote: >> >>> On 03/27/2017 07:02 AM, Carlo Alberto Ferraris wrote: >>>> This is a PoC patch that improves archive creation performance at >>> least in certain configurations >>> >>> What configuration performs poorly with sequential access? How much >>> improvement do you see with the patch, and why? >> >> I doubt that such methods will help to speed up archiving. I did many >> tests >> with similar approaches with star since aprox. 1997 and I did never see >> any >> performance win on any modern OS. > > Carlo's patch calls > posix_fadvise(fd, offset, len, > POSIX_FADV_WILLNEED|POSIX_FADV_SEQUENTIAL|POSIX_FADV_NOREUSE); > > According to > http://pubs.opengroup.org/onlinepubs/009695399/functions/posix_fadvise.html > "The advice to be applied to the data is specified by the advice parameter > and may be one of the following values: [lists various POSIX_FADV_xxx > definitions]" > > You can't bitwise OR several POSIX_FADV_xxx values together when calling > posix_fadvise(). Instead you would need to call posix_fadvise() three > times: > posix_fadvise(fd, offset, len, POSIX_FADV_WILLNEED); > posix_fadvise(fd, offset, len, POSIX_FADV_SEQUENTIAL); > posix_fadvise(fd, offset, len, POSIX_FADV_NOREUSE); > > Looking at Linux include/uapi/linux/fadvise.h bears that out; > POSIX_FADV_NOREUSE is 5, the same value as POSIX_FADV_DONTNEED | > POSIX_FADV_RANDOM. > > > Whether or not the OS does anything with posix_fadvise() hints is up to > the OS. But I seem to remember reading that Linux uses a larger read-ahead > if told that a file will be read sequentially. > > Both POSIX_FADV_WILLNEED and POSIX_FADV_SEQUENTIAL probably won't do any > harm, since they match the way in which tar reads files. > > For POSIX_FADV_NOREUSE, Linux currently treats that as a no-op, though a > patches was proposed a few years ago. > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/mm/fadvise.c?id=refs/tags/v4.10.6 > https://lwn.net/Articles/480930/ > > It might be a good idea to add an option to tar to use > POSIX_FADV_DONTNEED, since that could reduce tar's impact on other > processes (less filling the page cache with file data and evicting the > working set of other programs). > >
