Messages in this thread | | | Subject | Re: [PATCH v3 4/7] mm/compaction: update defer counter when allocation is expected to succeed | From | Vlastimil Babka <> | Date | Fri, 4 Dec 2015 17:52:21 +0100 |
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On 12/03/2015 08:11 AM, Joonsoo Kim wrote: > It's rather strange that compact_considered and compact_defer_shift aren't > updated but compact_order_failed is updated when allocation is expected > to succeed. Regardless actual allocation success, deferring for current > order will be disabled so it doesn't result in much difference to > compaction behaviour.
The difference is that if the defer reset was wrong, the next compaction attempt that fails would resume the deferred counters?
> Moreover, in the past, there is a gap between expectation for allocation > succeess in compaction and actual success in page allocator. But, now, > this gap would be diminished due to providing classzone_idx and alloc_flags > to watermark check in compaction and changed watermark check criteria > for high-order allocation. Therfore, it's not a big problem to update > defer counter when allocation is expected to succeed. This change > will help to simplify defer logic.
I guess that's true. But at least some experiment would be better.
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> > --- > include/linux/compaction.h | 2 -- > mm/compaction.c | 27 ++++++++------------------- > mm/page_alloc.c | 1 - > 3 files changed, 8 insertions(+), 22 deletions(-) >
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> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 7002c66..f3605fd 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2815,7 +2815,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > struct zone *zone = page_zone(page); > > zone->compact_blockskip_flush = false;
While we are here, I wonder if this is useful at all? compact_blockskip_flush is set true when scanners meet. That typically means the compaction wasn't successful. Rarely it can be, but I doubt this will make much difference, so we could remove this line as well.
> - compaction_defer_reset(zone, order, true); > count_vm_event(COMPACTSUCCESS); > return page; > } >
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