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

Dave Chinner
2014-05-20T06:33:51Z

On Mon, May 19, 2014 at 11:03:11PM -0700, Andrew Morton wrote:
> On Mon, 19 May 2014 22:59:15 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > 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".
>
> Or a new __GFP_FLAG.

Sure - and with that XFS will need another PF_ flag to tell the
memory allocator to set the new __GFP_FLAG on every allocation done
in that kworker task context, just like it uses PF_FSTRANS to ensure
that __GFP_NOFS is set for all the allocations in that kworker
context....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com