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From Qian Zhang <zhq527...@gmail.com>
Subject Re: Reconsidering `allocatable` check in the allocator
Date Wed, 07 Mar 2018 01:41:19 GMT
So if the input resources are "cpus:0.001,disk:1024", the `allocatable`
method will return "disk:1024"? This seems not compatible with the existing
behavior: with the current implementation of `allocatable`, the same input
resources will be just skipped because we think "cpus:0.001" is too small
for framework to launch a task.

allocatable = input
> foreach known resource type t: do
>   r = resources of type t from the input
>   if r is less than the min resource of type t; then
>     allocatable -= r
>   fi
> done
> return allocatable
>

Are we going to define min amount for each known resource type (including
disk and gpu)?


Regards,
Qian Zhang

On Wed, Mar 7, 2018 at 6:10 AM, Jie Yu <yujie.jay@gmail.com> wrote:

> Chatted with BenM offline on this. There's another option what both of us
> agreed that it's probably better than any of the ones mentioned above.
>
> The idea is to make `allocable` return the portion of the input resources
> that are allocatable, and strip the unelectable portion.
>
> For example:
> 1) If the input resources are "cpus:0.001,gpus:1", the `allocatable` method
> will return "gpus:1".
> 2) If the input resources are "cpus:1,mem:1", the `allocatable` method will
> return "cpus:1".
> 3) If the input resources are "cpus:0.001,mem:1", the `allocatable` method
> will return an empty Resources object.
>
> Basically, the algorithm is like the following:
>
> allocatable = input
> foreach known resource type t: do
>   r = resources of type t from the input
>   if r is less than the min resource of type t; then
>     allocatable -= r
>   fi
> done
> return allocatable
>
> Let me know what do you guys think!
>
> Thanks!
> - Jie
>
> On Fri, Mar 2, 2018 at 4:44 PM, Benjamin Mahler <bmahler@apache.org>
> wrote:
>
> > I think (2) would need to be:
> >
> > bool HierarchicalAllocatorProcess::allocatable(
> >     const Resources& resources)
> > {
> >   if (something outside {cpu, mem, disk} is present) return true
> >   else return true iff at least one of {cpu, mem, disk} has >= {MIN_CPU,
> > MIN_MEM, MIN_DISK}
> > }
> >
> > Otherwise, 1 GPU would be offered but 1GPU + 0.001 CPU would not?
> >
> > On Fri, Mar 2, 2018 at 9:27 AM, Jie Yu <yujie.jay@gmail.com> wrote:
> >
> > > Hi,
> > >
> > > The allocatable
> > > <https://github.com/apache/mesos/blob/1.5.x/src/master/alloc
> > > ator/mesos/hierarchical.cpp#L2471-L2479>
> > > check in the allocator (shown below) was originally introduced to help
> > > alleviate the situation where a framework receives some resources, but
> no
> > > cpu/memory, thus cannot launch a task.
> > >
> > > bool HierarchicalAllocatorProcess::allocatable(
> > >     const Resources& resources)
> > > {
> > >   Option<double> cpus = resources.cpus();
> > >   Option<Bytes> mem = resources.mem();
> > >
> > >   return (cpus.isSome() && cpus.get() >= MIN_CPUS) ||
> > >          (mem.isSome() && mem.get() >= MIN_MEM);
> > > }
> > >
> > > As pointed by Benjamin in MESOS-7398
> > > <https://issues.apache.org/jira/browse/MESOS-7398>, it now seems to
> > mainly
> > > help to minimize the performance overhead from too many small offers
> > > (instead too small resource amounts are kept out of the offer pool
> until
> > > they became accumulated into larger resources).
> > >
> > > This check does cause issues when new resources types are introduced.
> For
> > > instance, this check does prevent GPU resources alone from being
> > allocated
> > > to a framework. There are some other issues we discover MESOS-8626
> > > <https://issues.apache.org/jira/browse/MESOS-8626>.
> > >
> > > There are several proposals:
> > >
> > > (1) *Completely remove this check*. This check is a heuristic anyway,
> and
> > > only applies to a subset of resources (cpu/memory). However, there
> might
> > be
> > > some implication of that change since it's also leveraged to prevent
> too
> > > many small offers. *If you are concerned about this approach, please
> > raise
> > > your voice.*
> > >
> > > (2) *Consider adjust the check to the following. *
> > >
> > > bool HierarchicalAllocatorProcess::allocatable(
> > >     const Resources& resources)
> > > {
> > >   Option<double> cpus = resources.cpus();
> > >   Option<Bytes> mem = resources.mem();
> > >
> > >   if (cpus.isSome() && mem.isSome()) {
> > >     return cpus.get() >= MIN_CPUS || mem.get() >= MIN_MEM;
> > >   } else if (cpus.isSome()) {
> > >     return cpus.get() >= MIN_CPUS;
> > >   } else if (mem.isSome()) {
> > >     return mem.get() >= MIN_MEM;
> > >   } else {
> > >     return true;
> > >   }
> > > }
> > >
> > > Let me know what you think! Thanks!
> > >
> > > - Jie
> > >
> >
>

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