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

[Andrew Morton <akpm@linux-foundation.org>]

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.

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