Messages in this thread | | | Date | Wed, 11 Jun 2014 13:41:40 +0200 | From | Vlastimil Babka <> | Subject | Re: [PATCH 05/10] mm, compaction: remember position within pageblock in free pages scanner |
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On 06/11/2014 10:16 AM, Joonsoo Kim wrote: > On Wed, Jun 11, 2014 at 11:12:13AM +0900, Minchan Kim wrote: >> On Mon, Jun 09, 2014 at 11:26:17AM +0200, Vlastimil Babka wrote: >>> Unlike the migration scanner, the free scanner remembers the beginning of the >>> last scanned pageblock in cc->free_pfn. It might be therefore rescanning pages >>> uselessly when called several times during single compaction. This might have >>> been useful when pages were returned to the buddy allocator after a failed >>> migration, but this is no longer the case. >>> >>> This patch changes the meaning of cc->free_pfn so that if it points to a >>> middle of a pageblock, that pageblock is scanned only from cc->free_pfn to the >>> end. isolate_freepages_block() will record the pfn of the last page it looked >>> at, which is then used to update cc->free_pfn. >>> >>> In the mmtests stress-highalloc benchmark, this has resulted in lowering the >>> ratio between pages scanned by both scanners, from 2.5 free pages per migrate >>> page, to 2.25 free pages per migrate page, without affecting success rates. >>> >>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> >> Reviewed-by: Minchan Kim <minchan@kernel.org> >> >> Below is a nitpick. >> >>> Cc: Minchan Kim <minchan@kernel.org> >>> Cc: Mel Gorman <mgorman@suse.de> >>> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> >>> Cc: Michal Nazarewicz <mina86@mina86.com> >>> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> >>> Cc: Christoph Lameter <cl@linux.com> >>> Cc: Rik van Riel <riel@redhat.com> >>> Cc: David Rientjes <rientjes@google.com> >>> --- >>> mm/compaction.c | 33 ++++++++++++++++++++++++++++----- >>> 1 file changed, 28 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index 83f72bd..58dfaaa 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -297,7 +297,7 @@ static bool suitable_migration_target(struct page *page) >>> * (even though it may still end up isolating some pages). >>> */ >>> static unsigned long isolate_freepages_block(struct compact_control *cc, >>> - unsigned long blockpfn, >>> + unsigned long *start_pfn, >>> unsigned long end_pfn, >>> struct list_head *freelist, >>> bool strict) >>> @@ -306,6 +306,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, >>> struct page *cursor, *valid_page = NULL; >>> unsigned long flags; >>> bool locked = false; >>> + unsigned long blockpfn = *start_pfn; >>> >>> cursor = pfn_to_page(blockpfn); >>> >>> @@ -314,6 +315,9 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, >>> int isolated, i; >>> struct page *page = cursor; >>> >>> + /* Record how far we have got within the block */ >>> + *start_pfn = blockpfn; >>> + >> >> Couldn't we move this out of the loop for just one store?
Ah, I get it now. Ignore my previous reply.
> Hello, Vlastimil. > > Moreover, start_pfn can't be updated to end pfn with this approach. > Is it okay?
That's intentional, as end_pfn means the scanner would restart at the beginning of next pageblock. So I want to record last pfn *inside* the pageblock that was fully scanned. Note that there's a high change that fully scanning pageblock means that I haven't isolated enough and isolate_freepages() will advance to the previous pageblock anyway, and the recorded value will be overwritten. But still it's better to prevent this corner case.
So outside the loop, I would need to do:
*start_pfn = max(blockpfn, end_pfn - 1);
It looks a bit tricky but probably better than multiple assignments.
Thanks.
> Thanks. >
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