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

[Jacob Wen]

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....@oracle.com>
---
   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