Re: [PATCH v6 00/12] extend task comm from 16 to 24

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On Mon 2021-10-25 17:05:03, Steven Rostedt wrote:
> On Mon, 25 Oct 2021 11:10:09 -0700
> Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
> 
> > It looks like a churn that doesn't really address the problem.
> > If we were to allow long names then make it into a pointer and use 16 byte
> > as an optimized storage for short names. Any longer name would be a pointer.
> > In other words make it similar to dentry->d_iname.
> 
> That would be quite a bigger undertaking too, as it is assumed throughout
> the kernel that the task->comm is TASK_COMM_LEN and is nul terminated. And
> most locations that save the comm simply use a fixed size string of
> TASK_COMM_LEN. Not saying its not feasible, but it would require a lot more
> analysis of the impact by changing such a fundamental part of task struct
> from a static to something requiring allocation.

I fully agree. The evolution of this patchset clearly shows how many
code paths depend on the existing behavior.


> Unless you are suggesting that we truncate like normal the 16 byte names
> (to a max of 15 characters), and add a way to hold the entire name for
> those locations that understand it.

Yup. If the problem is only with kthreads, it might be possible to
store the pointer into "struct kthread" and update proc_task_name().
It would generalize the solution already used by workqueues.
I think that something like this was mentioned in the discussion
about v1.

Best Regards,
Petr



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