[PATCH v5 00/14] compaction: balancing overhead and success rates

From: Vlastimil Babka
Date: Mon Jul 28 2014 - 09:15:40 EST

Based on next-20140728.

Here's v5 of the series. I declared v4 ready on friday, so obviously I had to
immediately realize there's bug in one of the patches. So here's a new posting
with these changes:

- Patch 14 had two issues in v4. The major issue was leaking captured pages
when called from compact_pgdat() by kswapd. I thought that checking for
cc->order is enough to recognize a direct compaction, but missed that kswapd
also uses an order > 0 and does not consume any page. Fixed by adopting the
approach in original capture commit 1fb3f8ca0e92: cc->capture_page is no
longer a "struct page *", but "struct page **" and only when it's non-NULL
(in direct compaction) it means the caller wants a captured page pointer
filled there.

The minor issue was that during changes from v3 and v4, a rebase snafu lead
to removing the check whether to capture pages, based on matching pageblock
migratetype. So it could e.g. capture a page for UNMOVABLE allocation inside
a MOVABLE pageblock, which is undesired. So in v5 the check is back and
slightly improved by observing that if we want the whole pageblock, it does
not matter what its migratetype is.

- Patch 15 dropped for now (was always RFC), will appear in future series, as
it was negatively affecting extfrag. The (theoretical so far) explanation is
that by aggressively skipping a pageblock as soon as it cannot be completely
compacted, we fail to create lower-than-9-order free pages that could still
be otherwise created. Since page stealing works by stealing the
highest-order-available page and then satisfying potentially many allocations
from that, lack of high-order pages means more stealing events in potentially
more different pageblocks, so that many MOVABLE pageblocks are polluted, each
by only a few UNMOVABLE pages, which is still enough to kill the pageblocks
for the purposes of THP(-like) allocation.

- Patch 7 has benchmark data included.

- Checkpatch fixes applied, Acked-by's from Mel added.

David Rientjes (2):
mm: rename allocflags_to_migratetype for clarity
mm, compaction: pass gfp mask to compact_control

Vlastimil Babka (12):
mm, THP: don't hold mmap_sem in khugepaged when allocating THP
mm, compaction: defer each zone individually instead of preferred zone
mm, compaction: do not count compact_stall if all zones skipped
mm, compaction: do not recheck suitable_migration_target under lock
mm, compaction: move pageblock checks up from
mm, compaction: reduce zone checking frequency in the migration
mm, compaction: khugepaged should not give up due to need_resched()
mm, compaction: periodically drop lock and restore IRQs in scanners
mm, compaction: skip rechecks when lock was already held
mm, compaction: remember position within pageblock in free pages
mm, compaction: skip buddy pages by their order in the migrate scanner
mm, compaction: try to capture the just-created high-order freepage

include/linux/compaction.h | 28 +-
include/linux/gfp.h | 2 +-
mm/compaction.c | 757 ++++++++++++++++++++++++++++++++-------------
mm/huge_memory.c | 20 +-
mm/internal.h | 28 +-
mm/page_alloc.c | 189 ++++++++---
6 files changed, 733 insertions(+), 291 deletions(-)


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/