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    SubjectRe: [Ksummit-2010-discuss] checkpoint-restart: naked patch
    On Sat, 6 Nov 2010, Matt Helsley wrote:

    > Yes, our patches touch a wide variety of kernel code. You have just failed
    > to appreciate how "wide" the kernel ABI truly is. You can't really count
    > it by number of syscalls, number of pseudo-filesystems, etc. There's
    > also the intended behavior of those interfaces to consider. Each piece
    > of checkpoint/restart code is relatively self-contained. This can be
    > confirmed merely by looking at many of the patches we've already posted
    > enabling checkpoint/restart of that feature. Until you've tried to
    > implement checkpoint/restart for an interface or until you've bothered
    > to review a patch for one of them (my favorite on is eventfd:
    > ) please
    > don't tell us it's too complex. Then compare that with your proposed
    > ghastly stack of userspace cards -- ptrace (really more like strace) +
    > LD_PRELOAD + a daemon...
    > Incidentally, 20k lines of code is less than many pieces of the kernel.
    > It's less than many:
    > Filesystems (I've selected ones designed for rotating media or networks usually..)
    > ext4, nfs, ocfs2, xfs, reiserfs, ntfs, gfs2, jfs, cifs, ubifs, nilfs2, btrfs
    > Non-filesystem file-system support code:
    > nfsd, nls
    > It's less than one of the simpler DRM graphics drivers -- i915:
    > $ cd drivers/gpu/drm/i915
    > $ wc -l *.[ch]
    > ...
    > 41481 total
    > It's less than any one of the lpfc, bfa, aic7xxx, qla2xxx, and mpt2sas
    > drivers I see under scsi. Perhaps a more fair comparison might be to compare
    > a single driver to a single checkpointable kernel interface but it's
    > a more-fair comparison that skews even more in our favor.

    Please, do not compare things like single file systems, drivers, or
    otherwise fairly isolated components, with this "thing".
    This thing touches a freaky-large number of subsystems, effectively
    adding a glueage between them, which can might end up causing problems
    (and/or restrict design choices) in the future.
    The naked patch looks like just a sugar coating to me, which left out 300+
    lines of extra logic in epoll alone.
    This is one of the widest, deepest, intrusive patches I have seen in a
    while, whose inclusion would require a little bit more than handwaving and
    continuous re-posting IMO.

    - Davide

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