On 10/24/2014 05:00 AM, Joonsoo Kim wrote:
On Thu, Oct 23, 2014 at 10:39:45AM +0200, Vlastimil Babka wrote:
On 10/23/2014 10:15 AM, Joonsoo Kim wrote:
On Tue, Oct 14, 2014 at 01:53:44PM -0700, [email protected] wrote:
The patch titled
Subject: mm/compaction.c: avoid premature range skip in
isolate_migratepages_range
has been added to the -mm tree. Its filename is
mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch
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From: Joonsoo Kim <[email protected]>
Subject: mm/compaction.c: avoid premature range skip in
isolate_migratepages_range
commit edc2ca612496 ("mm, compaction: move pageblock checks up from
isolate_migratepages_range()") commonizes isolate_migratepages variants
and make them use isolate_migratepages_block().
isolate_migratepages_block() could stop the execution when enough pages
are isolated, but, there is no code in isolate_migratepages_range() to
handle this case. In the result, even if isolate_migratepages_block()
returns prematurely without checking all pages in the range,
isolate_migratepages_block() is called repeately on the following
pageblock and some pages in the previous range are skipped to check.
Then, CMA is failed frequently due to this fact.
To fix this problem, this patch let isolate_migratepages_range() know the
situation that enough pages are isolated and stop the isolation in that
case.
Note that isolate_migratepages() has no such problem, because, it always
stops the isolation after just one call of isolate_migratepages_block().
Signed-off-by: Joonsoo Kim <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Michal Nazarewicz <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Zhang Yanfei <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Sorry for the trouble. But I think a more robust and future-proof fix
would be a check such as: if (pfn < block_end_pfn) break;
This should catch any reason where isolate_migratepages_block() did not
finish whole pageblock, and which was not fatal enough to return pfn==0.
However currently this seems to happen only due to isolating too much,
so your patch should work.
So it's up to you if you want to make the check more generic now, or
later after this bug is fixed for 3.18.
'if (pfn < block_end_pfn) break;' has one problem.
If we have enough isolated pages and reach at block_end_pfn,
we can't stop with above check.
Oh, right.
More proper check may be as following.
'if (pfn < block_end_pfn ||
cc->nr_migratepages == COMPACT_CLUSTER_MAX) break;'
But, as you mentioned, there is no case where 'pfn < block_end_pfn'
now, so I'd like to remain the patch as is.
Yep, that would only make things uglier :/ So I'm for merging your patch
in 3.18 cycle to prevent breakage.
Thanks.
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