lkml.org 
[lkml]   [2010]   [Jun]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH 5/5] cpumask: reduce cpumask_size
    Date
    > On Mon, 28 Jun 2010 12:42:23 pm KOSAKI Motohiro wrote:
    > > > Now we're sure noone is using old cpumask operators, nor *cpumask, we can
    > > > allocate less bits safely. This reduces the memory usage of off-stack
    > > > cpumasks when CONFIG_CPUMASK_OFFSTACK=y but we don't have NR_CPUS actual
    > > > cpus.
    > >
    > > I have to say I'm sorry. Probably I broke your assumption.
    > > If this patch applied, we reintroduce exposing nr_cpu_ids issue and
    > > break libnuma again. I think following change is necessary too.
    > >
    > > Or, Am I missing something?
    >
    > I cc'd you because I remembered you being involved in that libnuma issue
    > and couldn't remember the details.
    >
    > Unfortunately, this solution doesn't work:
    >
    > > diff --git a/kernel/sched.c b/kernel/sched.c
    > > index 18faf4d..c14acad 100644
    > > --- a/kernel/sched.c
    > > +++ b/kernel/sched.c
    > > @@ -4823,7 +4823,9 @@ SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
    > >
    > > ret = sched_getaffinity(pid, mask);
    > > if (ret == 0) {
    > > - size_t retlen = min_t(size_t, len, cpumask_size());
    > > + size_t retlen = min_t(size_t, len,
    > > + BITS_TO_LONGS(NR_CPUS) * sizeof(long));
    > >
    >
    > Since mask is a cpumask_var_t, only cpumask_size() is allocated. We can't
    > copy NR_CPUS bits.

    Ahh, yes. It's purely broken.


    > But I think it's OK, anyway. libnuma is broken because it gets upset if the
    > number of cpus it reads from /sys/.../cpumap is more than the cpumask size
    > returned from sys_sched_getaffinity.
    >
    > Currently, getaffinity returns cpumask_size() (ie. based on NR_CPUS), and
    > the printing routines use nr_cpumask_bits (ie. based on NR_CPUS for
    > !CPUMASK_OFFSTACK, nr_cpu_ids for CPUMASK_OFFSTACK).
    >
    > (libnuma is OK on CONFIG_CPUMASK_OFFSTACK=y because the sysfs output is
    > *shorter* than expected. I checked the code).
    >
    > With this patch, cpumask_size() becomes based on nr_cpumask_bits, so both
    > getaffinity and sysfs are using the same basis.
    >
    > Do you agree?

    Sure. I agree I missed. Thank you for very kindful explanation!





    \
     
     \ /
      Last update: 2010-06-28 12:33    [W:0.024 / U:3.352 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site