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

[Konstantin Belousov]

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?

> 
> 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.