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Date: Mon, 23 Jun 2014 14:32:21 +0100
From: Mel Gorman <mgorman@...e.de>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>,
Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [patch 3/4] mm: vmscan: remove all_unreclaimable()
On Fri, Jun 20, 2014 at 12:33:49PM -0400, Johannes Weiner wrote:
> Direct reclaim currently calls shrink_zones() to reclaim all members
> of a zonelist, and if that wasn't successful it does another pass
> through the same zonelist to check overall reclaimability.
>
> Just check reclaimability in shrink_zones() directly and propagate the
> result through the return value. Then remove all_unreclaimable().
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
> mm/vmscan.c | 48 +++++++++++++++++++++++-------------------------
> 1 file changed, 23 insertions(+), 25 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ed1efb84c542..d0bc1a209746 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2244,9 +2244,10 @@ static inline bool should_continue_reclaim(struct zone *zone,
> }
> }
>
> -static void shrink_zone(struct zone *zone, struct scan_control *sc)
> +static unsigned long shrink_zone(struct zone *zone, struct scan_control *sc)
> {
> unsigned long nr_reclaimed, nr_scanned;
> + unsigned long zone_reclaimed = 0;
>
> do {
> struct mem_cgroup *root = sc->target_mem_cgroup;
> @@ -2290,8 +2291,12 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
> sc->nr_scanned - nr_scanned,
> sc->nr_reclaimed - nr_reclaimed);
>
> + zone_reclaimed += sc->nr_reclaimed - nr_reclaimed;
> +
> } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
> sc->nr_scanned - nr_scanned, sc));
> +
> + return zone_reclaimed;
> }
You do not actually need a counter here because all that matters is that
a page got reclaimed. It could just as easily have been
bool zone_reclaimable = false;
...
if (sc->nr_reclaimed - nr_reclaimed)
zone_reclaimable = true;
...
return zone_reclaimable
so that zone[s]_reclaimable is always a boolean and not sometimes a boolean
and sometimes a counter.
>
> /* Returns true if compaction should go ahead for a high-order request */
> @@ -2340,8 +2345,10 @@ static inline bool compaction_ready(struct zone *zone, int order)
> *
> * If a zone is deemed to be full of pinned pages then just give it a light
> * scan then give up on it.
> + *
> + * Returns whether the zones overall are reclaimable or not.
> */
Returns true if a zone was reclaimable
> -static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> +static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> {
> struct zoneref *z;
> struct zone *zone;
> @@ -2354,6 +2361,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> .gfp_mask = sc->gfp_mask,
> };
> enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
> + bool all_unreclaimable = true;
>
> /*
> * If the number of buffer_heads in the machine exceeds the maximum
> @@ -2368,6 +2376,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>
> for_each_zone_zonelist_nodemask(zone, z, zonelist,
> gfp_zone(sc->gfp_mask), sc->nodemask) {
> + unsigned long zone_reclaimed = 0;
> +
> if (!populated_zone(zone))
> continue;
> /*
> @@ -2414,10 +2424,15 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> &nr_soft_scanned);
> sc->nr_reclaimed += nr_soft_reclaimed;
> sc->nr_scanned += nr_soft_scanned;
> + zone_reclaimed += nr_soft_reclaimed;
> /* need some check for avoid more shrink_zone() */
> }
>
> - shrink_zone(zone, sc);
> + zone_reclaimed += shrink_zone(zone, sc);
> +
> + if (zone_reclaimed ||
> + (global_reclaim(sc) && zone_reclaimable(zone)))
> + all_unreclaimable = false;
> }
>
This is where you don't need the counter as such. It could just as
easily have been
bool reclaimable = false;
....
if (shrink_zone(zone, sc))
reclaimable = true;
if (!reclaimable && global_reclaim(sc) && zone_reclaimable(zone))
reclaimable = true;
return reclaimable;
It doesn't matter as such, it's just zone_reclaimed is implemented as a
counter but not used as one.
> /*
> @@ -2439,26 +2454,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> * promoted it to __GFP_HIGHMEM.
> */
> sc->gfp_mask = orig_mask;
> -}
>
> -/* All zones in zonelist are unreclaimable? */
> -static bool all_unreclaimable(struct zonelist *zonelist,
> - struct scan_control *sc)
> -{
> - struct zoneref *z;
> - struct zone *zone;
> -
> - for_each_zone_zonelist_nodemask(zone, z, zonelist,
> - gfp_zone(sc->gfp_mask), sc->nodemask) {
> - if (!populated_zone(zone))
> - continue;
> - if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
> - continue;
> - if (zone_reclaimable(zone))
> - return false;
> - }
> -
> - return true;
> + return !all_unreclaimable;
> }
>
> /*
> @@ -2482,6 +2479,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> {
> unsigned long total_scanned = 0;
> unsigned long writeback_threshold;
> + bool zones_reclaimable;
>
> delayacct_freepages_start();
>
> @@ -2492,7 +2490,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
> sc->priority);
> sc->nr_scanned = 0;
> - shrink_zones(zonelist, sc);
> + zones_reclaimable = shrink_zones(zonelist, sc);
>
> total_scanned += sc->nr_scanned;
> if (sc->nr_reclaimed >= sc->nr_to_reclaim)
> @@ -2533,8 +2531,8 @@ out:
> if (sc->compaction_ready)
> return 1;
>
> - /* top priority shrink_zones still had more to do? don't OOM, then */
> - if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
> + /* Any of the zones still reclaimable? Don't OOM. */
> + if (zones_reclaimable)
> return 1;
>
> return 0;
> --
> 2.0.0
>
--
Mel Gorman
SUSE Labs
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