Re: [PATCH] percpu: Sync vmalloc mappings in pcpu_alloc() and free_percpu()

Mathieu Desnoyers
2020-05-04T15:38:46Z

----- On May 4, 2020, at 11:31 AM, Joerg Roedel jroedel@suse.de wrote:

> On Mon, May 04, 2020 at 11:28:46AM -0400, Mathieu Desnoyers wrote:
>> ----- On May 4, 2020, at 11:12 AM, Joerg Roedel jroedel@suse.de wrote:
>> Placing this here is inefficient. It syncs mappings for each percpu allocation.
>> I would recommend moving it right after __vmalloc() is called to allocate the
>> underlying memory chunk instead:
>>
>> static void *pcpu_mem_zalloc(size_t size, gfp_t gfp)
>> {
>
> Tried this before, actually I put it into the caller of
> pcpu_mem_zalloc(), but that didn't fix the problem for me. Stevens
> test-case still hangs the machine.

That's unexpected.

Did you confirm that those hangs were also caused by percpu allocations ?

Maybe adding the vmalloc_sync_mappings() at each percpu allocation happens
to luckily sync mappings after some other vmalloc.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.