Re: [PATCH] devcoredump: increase the device delete timeout to 10 mins

[Abhinav Kumar]

Hi Johannes

On 2/12/2022 12:24 AM, Johannes Berg wrote:
> On Fri, 2022-02-11 at 23:52 -0800, Abhinav Kumar wrote:
> > The thread is writing the data to a file in local storage. From our
> > profiling, the read is the one taking the time not the write.
>
> That seems kind of hard to believe, let's say it's a 4/3 split (4
> minutes reading, 3 minutes writing, to make read > write as you say),
> and 3MiB size, that'd mean you get 12.8KiB/sec? That seems implausibly
> low, unless you're reading with really tiny buffers?
>
> Can you strace this somehow? (with timestamp info)

Yes, like I have already mentioned in earlier comments, we continue to 
check whats taking that long.

Once we find something from our analysis and also have the trace, will 
update the thread.

> > Just doubling what we have currently. I am not sure how the current 5
> > mins timeout came from.
>
> To be honest it came out of thin air, and wasn't really meant as a limit
> on how fast you can read (feels like even if it's tens of MiB you should
> read it in milliseconds into userspace), but more of a maximum time that
> we're willing to waste kernel memory if nobody is around to read the
> data.
>
> I thought it'd be better if we could somehow pin it while the userspace
> is reading it, but OTOH maybe that's actually bad, since that means
> userspace (though suitably privileged) could pin this kernel memory
> indefinitely.
>
> johannes