Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation

From: Alexander Shishkin
Date: Mon Sep 26 2016 - 12:13:30 EST

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:

> On Mon, Sep 26, 2016 at 11:27:08AM +0300, Alexander Shishkin wrote:
>> Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
>> > Well, we could 'force' inject a VMA into the process's address space, we
>> > do that for a few other things as well. It also makes for less
>> > exceptions with the actual core dumping.
>> Threads then will end up with the same buffer (through sharing the mm),
>> but they can't really share trace buffers.
>> Also, system core dump is still a problem.
> Hurm, true on both counts.

OTOH, system core dump buffers don't need inheritance or memlock

>> Or we can have per-cpu buffers for all user's tasks, record where each
>> task starts and ends in each buffer and cut out only bits relevant to
>> the task(s) that dump core.
> Which gets you the problem that when a task dumps core there might not
> be any state in the buffer, because the previous task flushed it all out
> :/

And also won't work with PMUs that don't generate PMIs, like ETMs.