Re: [PATCH 0/3] TLB flush multiple pages per IPI v5

Josh Boyer
2015-06-10T18:08:22Z

On Wed, Jun 10, 2015 at 12:42 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Wed, Jun 10, 2015 at 9:17 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> So anyway, I like the patch series. I just think that the final patch
>> - the one that actually saves the addreses, and limits things to
>> BATCH_TLBFLUSH_SIZE, should be limited.
>
> Oh, and another thing:
>
> Mel, can you please make that "struct tlbflush_unmap_batch" be just
> part of "struct task_struct" rather than a pointer?
>
> If you are worried about the cpumask size, you could use
>
> cpumask_var_t cpumask;
>
> and
>
> alloc_cpumask_var(..)
> ...
> free_cpumask_var(..)
>
> for that.
>
> That way, sane configurations never have the allocation cost.
>
> (Of course, sad to say, sane configurations are probably few and far
> between. At least Fedora seems to ship with a kernel where NR_CPU's is
> 1024 and thus CONFIG_CPUMASK_OFFSTACK=y. Oh well. What a waste of CPU
> cycles that is..)

The insane part being NR_CPUS = 1024? Or that to have said number
requires cpumask being dynamically allocated to avoid stack overflow?
(Or both I guess).

josh