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    SubjectRe: [2.6 patch] i386: always use 4k stacks
    On Sat, Dec 17, 2005 at 06:44:07PM +0100, Andi Kleen wrote:
    > Kyle Moffett <mrmacman_g4@mac.com> writes:
    >
    > > On Dec 16, 2005, at 10:35, Diego Calleja wrote:
    > > > I know, but there's too much resistance to the "pure" 4kb patch.
    > >
    > > I have yet to see any resistance to the 4Kb patch this time around
    > > that was not "*whine* don't break my ndiswrapper plz".
    >
    > My comment from last time about the missing safety net still applies 100%.
    >
    > Kernel code is getting more complex all the time and running with
    > very tight stack is just risky.

    My patch reduces it from roughly 6kB to 4kB.

    I'm with you that we need a safety net, but I don't see a problem with
    this being between 3kB and 4kB. The goal should be to _never_ use more
    than 3kB stack having a 1kB safety net.

    And in my experience, many stack problems don't come from code getting
    more complex but from people allocating 1kB structs or arrays of
    > 2k chars on the stack. In these cases, the code has to be fixed and
    "make checkstack" makes it easy to find such cases.

    And as a data point, my count of bug reports for problems with in-kernel
    code with 4k stacks after Neil's patch went into -mm is still at 0.

    > > The point is to force it in -mm so most people can't just disable it
    > > because it fixes their problem. We want 8k stacks to go away, and
    >
    > Who is we? And why?
    >
    > About the only half way credible arguments I've seen for it were:
    >
    > - "it might reduce stalls in the VM with order 1". Didn't quite
    > convince me because there were no numbers presented and at least on
    > x86-64 I've never noticed or got reported significant stalls because
    > of this.
    >
    > - "it allows more threads for 32bit which might run out of lowmem" - i
    > think everybody agrees that the 10k threads case is not really
    > something to encourage. And even when you want to add it then only a factor
    > two increase (which this patch brings) is not really too helpful.
    >...

    Unfortunately, "is not really something to encourage" doesn'a make
    "happens in real-life applications" impossible...

    Reducing the stack by one third brings a factor two reduction in the
    memory usage of threads - I wouldn't say this sounds too bad.

    > -Andi

    cu
    Adrian

    --

    "Is there not promise of rain?" Ling Tan asked suddenly out
    of the darkness. There had been need of rain for many days.
    "Only a promise," Lao Er said.
    Pearl S. Buck - Dragon Seed

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