The patch titled
Subject: mm, page_alloc: only use per-cpu allocator for irq-safe requests -fix
has been added to the -mm tree. Its filename is
mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix.patch
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From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, page_alloc: only use per-cpu allocator for irq-safe requests -fix
preempt_enable_no_resched() was used based on review feedback that had
no strong objection at the time. The thinking was that it avoided adding
a preemption point where one didn't exist before so the feedback was
applied. This reasoning was wrong.
There was an indirect preemption point as explained by Thomas Gleixner where
an interrupt could set_need_resched() followed by preempt_enable being
a preemption point that matters. This use of preempt_enable_no_resched
is bad from both a mainline and RT perspective and a violation of the
preemption mechanism. Peter Zijlstra noted that "the only acceptable use
of preempt_enable_no_resched() is if the next statement is a schedule()
variant".
The usage was outright broken and I should have stuck to preempt_enable()
as it was originally developed. It's known from previous tests
that there was no detectable difference to the performance by using
preempt_enable_no_resched().
This is a fix to the mmotm patch
mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch
Link: http://lkml.kernel.org/r/20170208143128.25ahymqlyspjcixu@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN mm/page_alloc.c~mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix
+++ a/mm/page_alloc.c
@@ -2517,7 +2517,7 @@ void free_hot_cold_page(struct page *pag
}
out:
- preempt_enable_no_resched();
+ preempt_enable();
}
/*
@@ -2683,7 +2683,7 @@ static struct page *rmqueue_pcplist(stru
__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
zone_statistics(preferred_zone, zone);
}
- preempt_enable_no_resched();
+ preempt_enable();
return page;
}
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-page_alloc-split-buffered_rmqueue.patch
mm-page_alloc-split-buffered_rmqueue-fix.patch
mm-page_alloc-split-alloc_pages_nodemask.patch
mm-page_alloc-drain-per-cpu-pages-from-workqueue-context.patch
mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch
mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix.patch
mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests-fix-v2.patch
mm-page_alloc-use-static-global-work_struct-for-draining-per-cpu-pages.patch
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