git: d1cbe7908986 - main - Allocating the LinuxKPI current structure from an interrupt thread must be done using the M_NOWAIT flag after 1ae20f7c70ea .

[Hans Petter Selasky]

On 3/11/21 8:04 PM, Konstantin Belousov wrote:
> On Thu, Mar 11, 2021 at 07:41:53PM +0100, Hans Petter Selasky wrote:
>> On 3/11/21 7:35 PM, Konstantin Belousov wrote:
>>> And I dislike this.  It is yet another case of introducing consumer-specific
>>> logic into core.  Isn't netepoch example enough?
>>>
>>> I presented another patch to Hans, where task and mm allocations are
>>> switched to zones, and the zones have reserve applied. Then allocations
>>> from ithreads use the reserve.
>>>
>>> There is one detail there, reserve is finite, for x86 I set it to the
>>> total limit of interrupts. This somewhat breaks if interrupts are
>>> deallocated and reallocated, but I think it is good enough even with
>>> this wart.
>>
>> Hi,
>>
>> Your patch doesn't address the issue of initializing the pointers in
>> question once. Still, for every call, we need to check if the pointer is
>> valid. This is not neccessary.
> I do not understand what you are saying there.
> Which pointers?  How does it not address?

Hi,

The current code calls linux_set_current() for every interrupt and timer 
callback. That means we continue to check td_lkpi_task for NULL for 
every one of these calls. Not strictly needed.

> 
>>
>> Also I don't see why we need to create a own UMA zone for these simple
>> structures. Won't the per-CPU sysctl consume more memory than the actual
>> task structures being allocated?
> Dedicated UMA zone allows to gracefully solve the requirement of non-failing
> allocation in non-sleepable context.  This is much simpler and cleaner than
> either trying to enumerate all existing ithreads or adding consumer-specific
> controls into generic kernel facility.
> 

Maybe I'm new to UMA zones. The M_USE_RESERVE can also be used with 
malloc() ?

--HPS