Re: [PATCH v3] mlx4_core: allocate ICM memory in page size chunks

[Tariq Toukan]

On 18/05/2018 12:45 AM, Qing Huang wrote:
> On 5/17/2018 2:14 PM, Eric Dumazet wrote:
> > On 05/17/2018 01:53 PM, Qing Huang wrote:
> > > When a system is under memory presure (high usage with fragments),
> > > the original 256KB ICM chunk allocations will likely trigger kernel
> > > memory management to enter slow path doing memory compact/migration
> > > ops in order to complete high order memory allocations.
> > >
> > > When that happens, user processes calling uverb APIs may get stuck
> > > for more than 120s easily even though there are a lot of free pages
> > > in smaller chunks available in the system.
> > >
> > > Syslog:
> > > ...
> > > Dec 10 09:04:51 slcc03db02 kernel: [397078.572732] INFO: task
> > > oracle_205573_e:205573 blocked for more than 120 seconds.
> > > ...
> > NACK on this patch.
> >
> > You have been asked repeatedly to use kvmalloc()
> >
> > This is not a minor suggestion.
> >
> > Take a look 
> > athttps://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d8c13f2271ec5178c52fbde072ec7b562651ed9d 
>
> Would you please take a look at how table->icm is being used in the mlx4 
> driver? It's a meta data used for individual pointer variable referencing,
> not as data frag or in/out buffer. It has no need for contiguous phy. 
> memory.
>
> Thanks.

NACK.

This would cause a degradation when iterating the entries of table->icm.
For example, in mlx4_table_get_range.

Thanks,
Tariq

> > And you'll understand some people care about this.
> >
> > Strongly.
> >
> > Thanks.