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Message-ID: <20140620202449.GA30849@cmpxchg.org>
Date: Fri, 20 Jun 2014 16:24:49 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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 Fri, Jun 20, 2014 at 06:56:03PM +0200, Vlastimil Babka wrote:
> 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>
Thanks, Vlastimil!
> > @@ -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.
This is a result of using emacs' auto-fill all the time when writing
comments, I have to watch my reflexes while moving stuff around :-)
Updated patch:
---
>From cd48b73fdca9e23aa21f65e9af1f850dbac5ab8e Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@...xchg.org>
Date: Wed, 11 Jun 2014 12:53:59 -0400
Subject: [patch] mm: vmscan: rework compaction-ready signaling in direct
reclaim
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>
---
mm/vmscan.c | 67 ++++++++++++++++++++++++++++---------------------------------
1 file changed, 31 insertions(+), 36 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 19b5b8016209..35747a75bf08 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.
+ */
+ 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 */
--
2.0.0
--
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