Re: [PATCH] mm/vmscan: Do not block forever at shrink_inactive_list().

Andrew Morton
2014-05-20T05:59:38Z

On Tue, 20 May 2014 10:44:49 +1000 Dave Chinner <david@fromorbit.com> wrote:

> @@ -258,14 +258,23 @@ xfs_bmapi_allocate_worker(
> struct xfs_bmalloca *args = container_of(work,
> struct xfs_bmalloca, work);
> unsigned long pflags;
> + unsigned long new_pflags = PF_FSTRANS;
>
> - /* we are in a transaction context here */
> - current_set_flags_nested(&pflags, PF_FSTRANS);
> + /*
> + * we are in a transaction context here, but may also be doing work
> + * in kswapd context, and hence we may need to inherit that state
> + * temporarily to ensure that we don't block waiting for memory reclaim
> + * in any way.
> + */
> + if (args->kswapd)
> + new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;

So current_is_kswapd() returns true for a thread which is not kswapd.
That's a bit smelly.

Should this thread really be incrementing KSWAPD_INODESTEAL instead of
PGINODESTEAL, for example? current_is_kswapd() does a range of things,
only one(?) of which you actually want.

It would be cleaner to create a new PF_ flag to select just that
behavior. That's a better model than telling the world "I am magic and
special".

But we're awfully close to running out of PF_ space and I don't know if
this ugly justifies consuming a flag.