Re: [PATCH] mm/vmscan: DRY cleanup for do_try_to_free_pages()

[Jacob Wen <jian.w.wen@xxxxxxxxxx>]

On 12/18/20 10:27 PM, Michal Hocko wrote:
> On Fri 18-12-20 21:51:48, Jacob Wen wrote:
> > On 12/18/20 6:51 PM, Michal Hocko wrote:
> > > On Fri 18-12-20 18:22:17, Jacob Wen wrote:
> > > > This patch reduces repetition of set_task_reclaim_state() around
> > > > do_try_to_free_pages().
> > > The changelog really should be talking about why this is needed/useful.
> > >   From the above it is not really clear whether you aimed at doing
> > > a clean up or this is a fix for some misbehavior. I do assume the former
> > > but this should be clearly articulated.
> > How about this?
> >
> > mm/vmscan: remove duplicate code around do_try_to_free_pages()
> >
> > This patch moves set_task_reclaim_state() into do_try_to_free_pages()
> > to avoid unnecessary repetition. It doesn't introduce functional
> > change.
> This is still more about what is changed more than why it is changed. I
> would go with something like the following:
> "
> reclaim_state has to be set for all reclaim paths because it acts as a
> storage to collect reclaim feedback. Currently set_task_reclaim_state is
> called from each highlevel reclaim function. Simplify the code flow by
> moving set_task_reclaim_state into core direct reclaim function
> (do_try_to_free_pages) for all direct reclaim paths.
> "
>
> To the patch itself. I am not opposed but I do not see an urgent reason
> to take it either. The net LOC increases slightly, it makes
> do_try_to_free_pages slightly more tricky due to different early return
> paths. Highlevel direct reclaim functions do not tend to change a lot.

set_task_reclaim_state() is a function with 3 lines of code of which 2 
lines contain WARN_ON_ONCE.

I am not comfortable with the current repetition.

> > > > Signed-off-by: Jacob Wen <jian.w.wen@xxxxxxxxxx>
> > > > ---
> > > >    mm/vmscan.c | 27 ++++++++++++++++-----------
> > > >    1 file changed, 16 insertions(+), 11 deletions(-)
> > > >
> > > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > > index 257cba79a96d..4bc244b23686 100644
> > > > --- a/mm/vmscan.c
> > > > +++ b/mm/vmscan.c
> > > > @@ -3023,6 +3023,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> > > >    	pg_data_t *last_pgdat;
> > > >    	struct zoneref *z;
> > > >    	struct zone *zone;
> > > > +	unsigned long ret;
> > > > +
> > > > +	set_task_reclaim_state(current, &sc->reclaim_state);
> > > > +
> > > >    retry:
> > > >    	delayacct_freepages_start();
> > > > @@ -3069,12 +3073,16 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> > > >    	delayacct_freepages_end();
> > > > -	if (sc->nr_reclaimed)
> > > > -		return sc->nr_reclaimed;
> > > > +	if (sc->nr_reclaimed) {
> > > > +		ret = sc->nr_reclaimed;
> > > > +		goto out;
> > > > +	}
> > > >    	/* Aborted reclaim to try compaction? don't OOM, then */
> > > > -	if (sc->compaction_ready)
> > > > -		return 1;
> > > > +	if (sc->compaction_ready) {
> > > > +		ret = 1;
> > > > +		goto out;
> > > > +	}
> > > >    	/*
> > > >    	 * We make inactive:active ratio decisions based on the node's
> > > > @@ -3101,7 +3109,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> > > >    		goto retry;
> > > >    	}
> > > > -	return 0;
> > > > +	ret = 0;
> > > > +out:
> > > > +	set_task_reclaim_state(current, NULL);
> > > > +	return ret;
> > > >    }
> > > >    static bool allow_direct_reclaim(pg_data_t *pgdat)
> > > > @@ -3269,13 +3280,11 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> > > >    	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
> > > >    		return 1;
> > > > -	set_task_reclaim_state(current, &sc.reclaim_state);
> > > >    	trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
> > > >    	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
> > > >    	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
> > > > -	set_task_reclaim_state(current, NULL);
> > > >    	return nr_reclaimed;
> > > >    }
> > > > @@ -3347,7 +3356,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> > > >    	 */
> > > >    	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
> > > > -	set_task_reclaim_state(current, &sc.reclaim_state);
> > > >    	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
> > > >    	noreclaim_flag = memalloc_noreclaim_save();
> > > > @@ -3355,7 +3363,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> > > >    	memalloc_noreclaim_restore(noreclaim_flag);
> > > >    	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
> > > > -	set_task_reclaim_state(current, NULL);
> > > >    	return nr_reclaimed;
> > > >    }
> > > > @@ -4023,11 +4030,9 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
> > > >    	fs_reclaim_acquire(sc.gfp_mask);
> > > >    	noreclaim_flag = memalloc_noreclaim_save();
> > > > -	set_task_reclaim_state(current, &sc.reclaim_state);
> > > >    	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
> > > > -	set_task_reclaim_state(current, NULL);
> > > >    	memalloc_noreclaim_restore(noreclaim_flag);
> > > >    	fs_reclaim_release(sc.gfp_mask);
> > > > --
> > > > 2.25.1