On Mon, Jun 23, 2014 at 03:36:37PM +0900, Minchan Kim wrote:
> On Fri, Jun 20, 2014 at 12:33:48PM -0400, 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 <han...@cmpxchg.org>
> Acked-by: Minchan Kim <minc...@kernel.org>
Thanks!
> > @@ -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
> > @@ -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 &&
>
> You are deleting comment sc->order <= PAGE_ALLOC_COSTLY_ORDER which was
> in compaction_ready. At least, that comment was useful for me to guess
> the intention. So if you have strong reason to remove that, I'd like to
> remain it.
There are two separate explanations for aborting reclaim early for
costly orders:
1. /* Do not consider compaction for orders reclaim is meant to satisfy */
2. /*
* 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.
*/
I thought it makes sense to pick one and go with that, so I went with
2. and moved the order check out there as well.
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