Subject: + mm-improve-documentation-of-page_order-v2.patch added to -mm tree
To: mgorman@xxxxxxx,aquini@xxxxxxxxxx,lauraa@xxxxxxxxxxxxxx,minchan@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 21 Jan 2014 11:56:28 -0800
The patch titled
Subject: mm: improve documentation of page_order
has been added to the -mm tree. Its filename is
mm-improve-documentation-of-page_order-v2.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-improve-documentation-of-page_order-v2.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-improve-documentation-of-page_order-v2.patch
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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.
[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 functions 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 being allocated in parallel and returning garbage as the order. If the
+ * caller does not hold page_zone(page)->lock, they 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-account-for-tlb-flushes-only-when-debugging-fix.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-hugetlbfs-add-some-vm_bug_ons-to-catch-non-hugetlbfs-pages.patch
mm-hugetlb-use-get_page_foll-in-follow_hugetlb_page.patch
mm-hugetlbfs-move-the-put-get_page-slab-and-hugetlbfs-optimization-in-a-faster-path.patch
mm-thp-optimize-compound_trans_huge.patch
mm-tail-page-refcounting-optimization-for-slab-and-hugetlbfs.patch
mm-hugetlbfs-use-__compound_tail_refcounted-in-__get_page_tail-too.patch
mm-hugetlbc-simplify-pageheadhuge-and-pagehuge.patch
mm-swapc-reorganize-put_compound_page.patch
mm-hugetlbc-defer-pageheadhuge-symbol-export.patch
mm-thp-__get_page_tail_foll-can-use-get_huge_page_tail.patch
mm-thp-turn-compound_head-into-bug_onpagetail-in-get_huge_page_tail.patch
mm-get-rid-of-unnecessary-pageblock-scanning-in-setup_zone_migrate_reserve.patch
mm-get-rid-of-unnecessary-pageblock-scanning-in-setup_zone_migrate_reserve-fix.patch
mm-call-mmu-notifiers-when-copying-a-hugetlb-page-range.patch
mm-show_mem-remove-show_mem_filter_page_count.patch
mm-show_mem-remove-show_mem_filter_page_count-fix.patch
memblock-numa-introduce-flags-field-into-memblock.patch
memblock-mem_hotplug-introduce-memblock_hotplug-flag-to-mark-hotpluggable-regions.patch
memblock-make-memblock_set_node-support-different-memblock_type.patch
acpi-numa-mem_hotplug-mark-hotpluggable-memory-in-memblock.patch
acpi-numa-mem_hotplug-mark-all-nodes-the-kernel-resides-un-hotpluggable.patch
memblock-mem_hotplug-make-memblock-skip-hotpluggable-regions-if-needed.patch
x86-numa-acpi-memory-hotplug-make-movable_node-have-higher-priority.patch
mm-rmap-recompute-pgoff-for-huge-page.patch
mm-rmap-factor-nonlinear-handling-out-of-try_to_unmap_file.patch
mm-rmap-factor-lock-function-out-of-rmap_walk_anon.patch
mm-rmap-make-rmap_walk-to-get-the-rmap_walk_control-argument.patch
mm-rmap-extend-rmap_walk_xxx-to-cope-with-different-cases.patch
mm-rmap-use-rmap_walk-in-try_to_unmap.patch
mm-rmap-use-rmap_walk-in-try_to_munlock.patch
mm-rmap-use-rmap_walk-in-page_referenced.patch
mm-rmap-use-rmap_walk-in-page_referenced-fix.patch
mm-rmap-use-rmap_walk-in-page_mkclean.patch
mm-page_alloc-allow-__gfp_nofail-to-allocate-below-watermarks-after-reclaim.patch
mm-numa-make-numa-migrate-related-functions-static.patch
mm-numa-limit-scope-of-lock-for-numa-migrate-rate-limiting.patch
mm-numa-trace-tasks-that-fail-migration-due-to-rate-limiting.patch
mm-numa-do-not-automatically-migrate-ksm-pages.patch
sched-add-tracepoints-related-to-numa-task-migration.patch
sched-add-tracepoints-related-to-numa-task-migration-fix.patch
mm-compaction-trace-compaction-begin-and-end.patch
mm-compaction-encapsulate-defer-reset-logic.patch
mm-compaction-reset-cached-scanner-pfns-before-reading-them.patch
mm-compaction-detect-when-scanners-meet-in-isolate_freepages.patch
mm-compaction-do-not-mark-unmovable-pageblocks-as-skipped-in-async-compaction.patch
mm-compaction-reset-scanner-positions-immediately-when-they-meet.patch
mm-page_alloc-warn-for-non-blockable-__gfp_nofail-allocation-failure.patch
mm-migrate-add-comment-about-permanent-failure-path.patch
mm-migrate-correct-failure-handling-if-hugepage_migration_support.patch
mm-migrate-remove-putback_lru_pages-fix-comment-on-putback_movable_pages.patch
mm-migrate-remove-unused-function-fail_migrate_page.patch
mm-munlock-fix-potential-race-with-thp-page-split.patch
numa-add-a-sysctl-for-numa_balancing.patch
numa-add-a-sysctl-for-numa_balancing-fix.patch
mm-vmscan-shrink-all-slab-objects-if-tight-on-memory.patch
mm-vmscan-call-numa-unaware-shrinkers-irrespective-of-nodemask.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-show-message-when-updating-min_free_kbytes-in-thp.patch
mm-improve-documentation-of-page_order-v2.patch
mm-improve-documentation-of-page_order-v2-fix.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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