Subject: + fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch added to -mm tree
To: mgorman@xxxxxxx,dave.hansen@xxxxxxxxx,hannes@xxxxxxxxxxx,hughd@xxxxxxxxxx,jack@xxxxxxx,mhocko@xxxxxxx,oleg@xxxxxxxxxx,paulmck@xxxxxxxxxxxxxxxxxx,peterz@xxxxxxxxxxxxx,riel@xxxxxxxxxx,tytso@xxxxxxx,vbabka@xxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 13 May 2014 15:41:10 -0700
The patch titled
Subject: fs: buffer: do not use unnecessary atomic operations when discarding buffers
has been added to the -mm tree. Its filename is
fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch
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From: Mel Gorman <mgorman@xxxxxxx>
Subject: fs: buffer: do not use unnecessary atomic operations when discarding buffers
Discarding buffers uses a bunch of atomic operations when discarding
buffers because ...... I can't think of a reason. Use a cmpxchg loop to
clear all the necessary flags. In most (all?) cases this will be a single
atomic operations.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/buffer.c | 14 +++++++++-----
include/linux/buffer_head.h | 5 +++++
2 files changed, 14 insertions(+), 5 deletions(-)
diff -puN fs/buffer.c~fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers fs/buffer.c
--- a/fs/buffer.c~fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers
+++ a/fs/buffer.c
@@ -1485,14 +1485,18 @@ EXPORT_SYMBOL(set_bh_page);
*/
static void discard_buffer(struct buffer_head * bh)
{
+ unsigned long b_state, b_state_old;
+
lock_buffer(bh);
clear_buffer_dirty(bh);
bh->b_bdev = NULL;
- clear_buffer_mapped(bh);
- clear_buffer_req(bh);
- clear_buffer_new(bh);
- clear_buffer_delay(bh);
- clear_buffer_unwritten(bh);
+ b_state = bh->b_state;
+ for (;;) {
+ b_state_old = cmpxchg(&bh->b_state, b_state, (b_state & ~BUFFER_FLAGS_DISCARD));
+ if (b_state_old == b_state)
+ break;
+ b_state = b_state_old;
+ }
unlock_buffer(bh);
}
diff -puN include/linux/buffer_head.h~fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers include/linux/buffer_head.h
--- a/include/linux/buffer_head.h~fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers
+++ a/include/linux/buffer_head.h
@@ -77,6 +77,11 @@ struct buffer_head {
atomic_t b_count; /* users using this buffer_head */
};
+/* Bits that are cleared during an invalidate */
+#define BUFFER_FLAGS_DISCARD \
+ (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
+ 1 << BH_Delay | 1 << BH_Unwritten)
+
/*
* macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
* and buffer_foo() functions.
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
x86-require-x86-64-for-automatic-numa-balancing.patch
x86-define-_page_numa-by-reusing-software-bits-on-the-pmd-and-pte-levels.patch
x86-define-_page_numa-by-reusing-software-bits-on-the-pmd-and-pte-levels-fix-2.patch
mm-introduce-do_shared_fault-and-drop-do_fault-fix-fix.patch
mm-compactionc-isolate_freepages_block-small-tuneup.patch
mm-only-force-scan-in-reclaim-when-none-of-the-lrus-are-big-enough.patch
mm-huge_memoryc-complete-conversion-to-pr_foo.patch
mm-disable-zone_reclaim_mode-by-default.patch
mm-page_alloc-do-not-cache-reclaim-distances.patch
mm-page_alloc-do-not-cache-reclaim-distances-fix.patch
mm-page_alloc-prevent-migrate_reserve-pages-from-being-misplaced.patch
mm-compaction-clean-up-unused-code-lines.patch
mm-compaction-cleanup-isolate_freepages.patch
mm-compaction-cleanup-isolate_freepages-fix.patch
mm-compaction-cleanup-isolate_freepages-fix-2.patch
mm-compaction-cleanup-isolate_freepages-fix3.patch
mm-swapc-clean-up-lru_cache_add-functions.patch
mm-vmscan-do-not-throttle-based-on-pfmemalloc-reserves-if-node-has-no-zone_normal.patch
mm-vmscan-do-not-throttle-based-on-pfmemalloc-reserves-if-node-has-no-zone_normal-checkpatch-fixes.patch
mm-vmscan-do-not-throttle-based-on-pfmemalloc-reserves-if-node-has-no-zone_normal-fix.patch
mm-numa-add-migrated-transhuge-pages-to-lru-the-same-way-as-base-pages.patch
mm-swapc-introduce-put_refcounted_compound_page-helpers-for-spliting-put_compound_page.patch
mm-swapc-split-put_compound_page-function.patch
mm-introdule-compound_head_by_tail.patch
mm-x86-pgtable-drop-unneeded-preprocessor-ifdef.patch
mm-x86-pgtable-require-x86_64-for-soft-dirty-tracker.patch
mm-mempolicyc-parameter-doc-uniformization.patch
mm-migration-add-destination-page-freeing-callback.patch
mm-compaction-return-failed-migration-target-pages-back-to-freelist.patch
mm-compaction-add-per-zone-migration-pfn-cache-for-async-compaction.patch
mm-compaction-embed-migration-mode-in-compact_control.patch
mm-thp-avoid-excessive-compaction-latency-during-fault.patch
mm-thp-avoid-excessive-compaction-latency-during-fault-fix.patch
mm-compaction-terminate-async-compaction-when-rescheduling.patch
mm-compaction-do-not-count-migratepages-when-unnecessary.patch
mm-compaction-avoid-rescanning-pageblocks-in-isolate_freepages.patch
swap-change-swap_info-singly-linked-list-to-list_head.patch
plist-add-helper-functions.patch
plist-add-plist_requeue.patch
swap-change-swap_list_head-to-plist-add-swap_avail_head.patch
mm-page_alloc-do-not-update-zlc-unless-the-zlc-is-active.patch
mm-page_alloc-do-not-treat-a-zone-that-cannot-be-used-for-dirty-pages-as-full.patch
jump_label-expose-the-reference-count.patch
mm-page_alloc-use-jump-labels-to-avoid-checking-number_of_cpusets.patch
mm-page_alloc-only-check-the-zone-id-check-if-pages-are-buddies.patch
mm-page_alloc-only-check-the-alloc-flags-and-gfp_mask-for-dirty-once.patch
mm-page_alloc-take-the-alloc_no_watermark-check-out-of-the-fast-path.patch
mm-page_alloc-use-word-based-accesses-for-get-set-pageblock-bitmaps.patch
mm-page_alloc-reduce-number-of-times-page_to_pfn-is-called.patch
mm-page_alloc-lookup-pageblock-migratetype-with-irqs-enabled-during-free.patch
mm-page_alloc-use-unsigned-int-for-order-in-more-places.patch
mm-page_alloc-convert-hot-cold-parameter-and-immediate-callers-to-bool.patch
mm-shmem-avoid-atomic-operation-during-shmem_getpage_gfp.patch
mm-do-not-use-atomic-operations-when-releasing-pages.patch
mm-do-not-use-unnecessary-atomic-operations-when-adding-pages-to-the-lru.patch
fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers.patch
fs-buffer-do-not-use-unnecessary-atomic-operations-when-discarding-buffers-fix.patch
mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possible.patch
mm-page_alloc-debug_vm-checks-for-free_list-placement-of-cma-and-reserve-pages.patch
do_shared_fault-check-that-mmap_sem-is-held.patch
smp-print-more-useful-debug-info-upon-receiving-ipi-on-an-offline-cpu.patch
smp-print-more-useful-debug-info-upon-receiving-ipi-on-an-offline-cpu-fix.patch
cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu.patch
cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v3.patch
linux-next.patch
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