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    SubjectRe: [GIT PULL v2] Early SLAB fixes for 2.6.31
    On Tue, Jun 16, 2009 at 03:28:07PM +1000, Benjamin Herrenschmidt wrote:
    > On Tue, 2009-06-16 at 06:57 +0200, Nick Piggin wrote:
    > >
    > > Yes but that's heavily qualified. As I said, we already require
    > > a lot of knowledge of context passed in to it. I have no interest
    > > in adding code to make *early boot* code not have to care about
    > > that, especially because everybody else certainly has to know
    > > whether they are calling the allocator with interrupts disabled
    > > or a lock held etc.
    > You seem to totally ignore the argument I made to answer this specific
    > point in one of my previous emails. Right, they are to some extent
    > subjective, but I believe they have some standing. The main one is
    > probably that it's a lot less obvious to a lot of code where in the boot
    > process it's going to be called, or even if it's going to be called at
    > boot, later, both. This is especially true nowadays with all the talks
    > about shuffling more of the boot process around.

    I didn't ignore that argument, I just don't agree. It only does
    not "know" the context it is called from if it does not get that
    information passed to it from its caller who does know.

    > > To be clear about this: the allocator is fully servicable and
    > > no different to normal system running at this point. The
    > > difference for example is that code runs with interrupts off
    > > but incorrectly uses GFP_KERNEL for allocations. This is a
    > > blatent bug in any other kernel code, I don't know why boot
    > > code is OK to be horrible and wrong and work around it with
    > > the equally horrible system_state (and this gfp mask which is
    > > just system_state under another name).
    > Because it would be extremely impractical to have to explicitely pass
    > the gfp_flags around for anything that can be called at boot time. This
    > is as simple as that. A -lot- more impractical than requiring atomic
    > call sites to know what they are doing.

    We'll see.

    > > I just don't want to use this slab fix in question to be a
    > > license to throw away and forget all about any context information
    > > in the early boot code because someone asserts "it will make the
    > > code better". I'm fine with the slab change for now, but let's
    > > try to retain context information as well.
    > But in many case it's meaningless. Again, what do you define as "boot"
    > is a very obscure thing here.

    It's not obscure. I'm vague because it doesn't matter *all that much*.

    > > If somebody comes up with a patch to remove thousands of lines
    > > of boot code by ignoring context, then I might concede the
    > > point and we could remove the context annotations.
    > No, we don't want to -add- thousands of lines of code :-) And we can

    I don't understand. Where would you be adding thousands of lines
    of code?

    > indeed remove a bunch of the old slab_is_available() tests too indeed.
    > And no, they should not -all- be converted to NOWAIT. See vmalloc() as a
    > good example, I have a few more like that.

    There aren't too many significant code simplifications AFAIKS.

     \ /
      Last update: 2009-06-16 07:39    [W:0.023 / U:18.120 seconds]
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