Re: [PATCH 1/2] x86: Cleanup TIF value gaps in shift range

David Rientjes
2010-10-18T20:48:06Z

On Mon, 18 Oct 2010, Frederic Weisbecker wrote:

> 9, 19 and 26 values are missing from the TIF shift range, probably
> due to flags that were removed by the past. Now repack the range
> so that we can quickly retrieve the remaining free shift slots.
>
> But take care of keeping the seperation between high and low bits
> as some masks are created on top of this boundary.
>

What's the benefit of doing this?

These flags are exported to userspace through SysRq-T, SysRq+W, the hung
task detector, and the rcu stall detector, so there may be external
dependencies testing for these bits.

We use this to look for TIF_MEMDIE to determine whether an oom killed task
has failed to exit and becomes hung after having access to memory
reserves, and that's one of the bits you've changed here.