On Tuesday 09 October 2012 12:11:43 Mel Gorman wrote:
> On Tue, Oct 09, 2012 at 10:40:10AM +0200, Bartlomiej Zolnierkiewicz wrote:
> > I also need following patch to make CONFIG_CMA=y && CONFIG_COMPACTION=y case
> > work:
> >
> > From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
> > Subject: [PATCH] mm: compaction: cache if a pageblock was scanned and no pages were isolated - cma fix
> >
> > Patch "mm: compaction: cache if a pageblock was scanned and no pages
> > were isolated" needs a following fix to successfully boot next-20121002
> > kernel (same with next-20121008) with CONFIG_CMA=y and CONFIG_COMPACTION=y
> > (with applied -fix1, -fix2, -fix3 patches from Mel Gorman and also with
> > cmatest module from Thierry Reding compiled in).
> >
>
> Why is it needed to make it boot? CMA should not care about the
It boots without Thierry's cmatest module but then fails on CMA
allocation attempt (I used out-of-tree /dev/cma_test interface to
generate CMA allocation request from user-space).
> PG_migrate_skip hint being set because it should always ignore it in
> alloc_contig_range() due to cc->ignore_skip_hint. It's not obvious to
> me why this fixes a boot failure and I wonder if it's papering over some
> underlying problem. Can you provide more details please?
I just compared CONFIG_COMPACTION=n and =y cases initially, figured
out the difference and did the change. However on a closer look it
seems that {get,clear,set}_pageblock_skip() use incorrect bit ranges
(please compare to bit ranges used by {get,set}_pageblock_flags()
used for migration types) and can overwrite pageblock migratetype of
the next pageblock in the bitmap (I wonder how could this code ever
worked before?).
> > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
> > Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> > ---
> > mm/compaction.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > Index: b/mm/compaction.c
> > ===================================================================
> > --- a/mm/compaction.c 2012-10-08 18:10:53.491679716 +0200
> > +++ b/mm/compaction.c 2012-10-08 18:11:33.615679713 +0200
> > @@ -117,7 +117,8 @@ static void update_pageblock_skip(struct
> > bool migrate_scanner)
> > {
> > struct zone *zone = cc->zone;
> > - if (!page)
> > +
> > + if (!page || cc->ignore_skip_hint)
> > return;
> >
> > if (!nr_isolated) {
The patch below also fixes the issue for me:
From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Subject: [PATCH] mm: compaction: fix bit ranges in {get,clear,set}_pageblock_skip()
{get,clear,set}_pageblock_skip() use incorrect bit ranges (please compare
to bit ranges used by {get,set}_pageblock_flags() used for migration types)
and can overwrite pageblock migratetype of the next pageblock in the bitmap.
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
---
include/linux/pageblock-flags.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
Index: b/include/linux/pageblock-flags.h
===================================================================
--- a/include/linux/pageblock-flags.h 2012-10-09 12:50:20.366340001 +0200
+++ b/include/linux/pageblock-flags.h 2012-10-09 12:50:31.794339996 +0200
@@ -71,13 +71,13 @@ void set_pageblock_flags_group(struct pa
#ifdef CONFIG_COMPACTION
#define get_pageblock_skip(page) \
get_pageblock_flags_group(page, PB_migrate_skip, \
- PB_migrate_skip + 1)
+ PB_migrate_skip)
#define clear_pageblock_skip(page) \
set_pageblock_flags_group(page, 0, PB_migrate_skip, \
- PB_migrate_skip + 1)
+ PB_migrate_skip)
#define set_pageblock_skip(page) \
set_pageblock_flags_group(page, 1, PB_migrate_skip, \
- PB_migrate_skip + 1)
+ PB_migrate_skip)
#endif /* CONFIG_COMPACTION */
#define get_pageblock_flags(page) \
--
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