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Message-ID: <53A467A3.1050008@suse.cz>
Date: Fri, 20 Jun 2014 18:56:03 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Johannes Weiner <hannes@...xchg.org>,
Andrew Morton <akpm@...ux-foundation.org>
CC: Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [patch 2/4] mm: vmscan: rework compaction-ready signaling in
direct reclaim
On 06/20/2014 06:33 PM, Johannes Weiner wrote:
> Page reclaim for a higher-order page runs until compaction is ready,
> then aborts and signals this situation through the return value of
> shrink_zones(). This is an oddly specific signal to encode in the
> return value of shrink_zones(), though, and can be quite confusing.
>
> Introduce sc->compaction_ready and signal the compactability of the
> zones out-of-band to free up the return value of shrink_zones() for
> actual zone reclaimability.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
(with a nitpick below)
> ---
> mm/vmscan.c | 67 ++++++++++++++++++++++++++++---------------------------------
> 1 file changed, 31 insertions(+), 36 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 19b5b8016209..ed1efb84c542 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -65,6 +65,9 @@ struct scan_control {
> /* Number of pages freed so far during a call to shrink_zones() */
> unsigned long nr_reclaimed;
>
> + /* One of the zones is ready for compaction */
> + int compaction_ready;
> +
> /* How many pages shrink_list() should reclaim */
> unsigned long nr_to_reclaim;
>
> @@ -2292,15 +2295,11 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
> }
>
> /* Returns true if compaction should go ahead for a high-order request */
> -static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
> +static inline bool compaction_ready(struct zone *zone, int order)
> {
> unsigned long balance_gap, watermark;
> bool watermark_ok;
>
> - /* Do not consider compaction for orders reclaim is meant to satisfy */
> - if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
> - return false;
> -
> /*
> * Compaction takes time to run and there are potentially other
> * callers using the pages just freed. Continue reclaiming until
> @@ -2309,18 +2308,18 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
> */
> balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
> zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
> - watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
> + watermark = high_wmark_pages(zone) + balance_gap + (2UL << order);
> watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
>
> /*
> * If compaction is deferred, reclaim up to a point where
> * compaction will have a chance of success when re-enabled
> */
> - if (compaction_deferred(zone, sc->order))
> + if (compaction_deferred(zone, order))
> return watermark_ok;
>
> /* If compaction is not ready to start, keep reclaiming */
> - if (!compaction_suitable(zone, sc->order))
> + if (!compaction_suitable(zone, order))
> return false;
>
> return watermark_ok;
> @@ -2341,20 +2340,14 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
> *
> * If a zone is deemed to be full of pinned pages then just give it a light
> * scan then give up on it.
> - *
> - * This function returns true if a zone is being reclaimed for a costly
> - * high-order allocation and compaction is ready to begin. This indicates to
> - * the caller that it should consider retrying the allocation instead of
> - * further reclaim.
> */
> -static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> +static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> {
> struct zoneref *z;
> struct zone *zone;
> unsigned long nr_soft_reclaimed;
> unsigned long nr_soft_scanned;
> unsigned long lru_pages = 0;
> - bool aborted_reclaim = false;
> struct reclaim_state *reclaim_state = current->reclaim_state;
> gfp_t orig_mask;
> struct shrink_control shrink = {
> @@ -2391,22 +2384,24 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> if (sc->priority != DEF_PRIORITY &&
> !zone_reclaimable(zone))
> continue; /* Let kswapd poll it */
> - if (IS_ENABLED(CONFIG_COMPACTION)) {
> - /*
> - * If we already have plenty of memory free for
> - * compaction in this zone, don't free any more.
> - * Even though compaction is invoked for any
> - * non-zero order, only frequent costly order
> - * reclamation is disruptive enough to become a
> - * noticeable problem, like transparent huge
> - * page allocations.
> - */
> - if ((zonelist_zone_idx(z) <= requested_highidx)
> - && compaction_ready(zone, sc)) {
> - aborted_reclaim = true;
> - continue;
> - }
> +
> + /*
> + * If we already have plenty of memory free
> + * for compaction in this zone, don't free any
> + * more. Even though compaction is invoked
> + * for any non-zero order, only frequent
> + * costly order reclamation is disruptive
> + * enough to become a noticeable problem, like
> + * transparent huge page allocations.
> + */
You moved this comment block left, yet you further shortened the individual lines, despite
there is now more space to prolong them.
> + if (IS_ENABLED(CONFIG_COMPACTION) &&
> + sc->order > PAGE_ALLOC_COSTLY_ORDER &&
> + zonelist_zone_idx(z) <= requested_highidx &&
> + compaction_ready(zone, sc->order)) {
> + sc->compaction_ready = true;
> + continue;
> }
> +
> /*
> * This steals pages from memory cgroups over softlimit
> * and returns the number of reclaimed pages and
> @@ -2444,8 +2439,6 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> * promoted it to __GFP_HIGHMEM.
> */
> sc->gfp_mask = orig_mask;
> -
> - return aborted_reclaim;
> }
>
> /* All zones in zonelist are unreclaimable? */
> @@ -2489,7 +2482,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> {
> unsigned long total_scanned = 0;
> unsigned long writeback_threshold;
> - bool aborted_reclaim;
>
> delayacct_freepages_start();
>
> @@ -2500,12 +2492,15 @@ 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;
> - aborted_reclaim = shrink_zones(zonelist, sc);
> + shrink_zones(zonelist, sc);
>
> total_scanned += sc->nr_scanned;
> if (sc->nr_reclaimed >= sc->nr_to_reclaim)
> goto out;
>
> + if (sc->compaction_ready)
> + goto out;
> +
> /*
> * If we're getting trouble reclaiming, start doing
> * writepage even in laptop mode.
> @@ -2526,7 +2521,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> WB_REASON_TRY_TO_FREE_PAGES);
> sc->may_writepage = 1;
> }
> - } while (--sc->priority >= 0 && !aborted_reclaim);
> + } while (--sc->priority >= 0);
>
> out:
> delayacct_freepages_end();
> @@ -2535,7 +2530,7 @@ out:
> return sc->nr_reclaimed;
>
> /* Aborted reclaim to try compaction? don't OOM, then */
> - if (aborted_reclaim)
> + if (sc->compaction_ready)
> return 1;
>
> /* top priority shrink_zones still had more to do? don't OOM, then */
>
--
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