Subject: [merged] mm-improve-documentation-of-page_order-v2.patch removed from -mm tree
To: mgorman@xxxxxxx,aquini@xxxxxxxxxx,lauraa@xxxxxxxxxxxxxx,minchan@xxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Fri, 24 Jan 2014 10:59:43 -0800
The patch titled
Subject: mm: improve documentation of page_order
has been removed from the -mm tree. Its filename was
mm-improve-documentation-of-page_order-v2.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxx>
Subject: mm: improve documentation of page_order
Developers occasionally try and optimise PFN scanners by using page_order
but miss that in general it requires zone->lock. This has happened twice
for compaction.c and rejected both times. This patch clarifies the
documentation of page_order and adds a note to compaction.c why page_order
is not used.
[akpm@xxxxxxxxxxxxxxxxxxxx: tweaks]
[lauraa@xxxxxxxxxxxxxx: Corrected a page_zone(page)->lock reference]
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 5 ++++-
mm/internal.h | 8 +++++---
2 files changed, 9 insertions(+), 4 deletions(-)
diff -puN mm/compaction.c~mm-improve-documentation-of-page_order-v2 mm/compaction.c
--- a/mm/compaction.c~mm-improve-documentation-of-page_order-v2
+++ a/mm/compaction.c
@@ -523,7 +523,10 @@ isolate_migratepages_range(struct zone *
if (!isolation_suitable(cc, page))
goto next_pageblock;
- /* Skip if free */
+ /*
+ * Skip if free. page_order cannot be used without zone->lock
+ * as nothing prevents parallel allocations or buddy merging.
+ */
if (PageBuddy(page))
continue;
diff -puN mm/internal.h~mm-improve-documentation-of-page_order-v2 mm/internal.h
--- a/mm/internal.h~mm-improve-documentation-of-page_order-v2
+++ a/mm/internal.h
@@ -143,9 +143,11 @@ isolate_migratepages_range(struct zone *
#endif
/*
- * function for dealing with page's order in buddy system.
- * zone->lock is already acquired when we use these.
- * So, we don't need atomic page->flags operations here.
+ * This function returns the order of a free page in the buddy system. In
+ * general, page_zone(page)->lock must be held by the caller to prevent the
+ * page from being allocated in parallel and returning garbage as the order.
+ * If a caller does not hold page_zone(page)->lock, it must guarantee that the
+ * page cannot be allocated or merged in parallel.
*/
static inline unsigned long page_order(struct page *page)
{
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
origin.patch
mm-remove-bug_on-from-mlock_vma_page.patch
x86-mm-account-for-tlb-flushes-only-when-debugging.patch
x86-mm-clean-up-inconsistencies-when-flushing-tlb-ranges.patch
x86-mm-eliminate-redundant-page-table-walk-during-tlb-range-flushing.patch
x86-mm-change-tlb_flushall_shift-for-ivybridge.patch
mm-x86-revisit-tlb_flushall_shift-tuning-for-page-flushes-except-on-ivybridge.patch
mm-page_alloc-allow-__gfp_nofail-to-allocate-below-watermarks-after-reclaim.patch
mm-vmscan-respect-numa-policy-mask-when-shrinking-slab-on-direct-reclaim.patch
mm-vmscan-move-call-to-shrink_slab-to-shrink_zones.patch
mm-vmscan-remove-shrink_control-arg-from-do_try_to_free_pages.patch
mm-compaction-ignore-pageblock-skip-when-manually-invoking-compaction.patch
linux-next.patch
mm-migratec-fix-setting-of-cpupid-on-page-migration-twice-against-normal-page.patch
zsmalloc-move-it-under-mm.patch
zram-promote-zram-from-staging.patch
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