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>
---
fs/buffer.c | 14 +++++++++-----
include/linux/buffer_head.h | 5 +++++
2 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 9ddb9fc..e80012d 100644
--- a/fs/buffer.c
+++ b/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 --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index c40302f..95f565a 100644
--- a/include/linux/buffer_head.h
+++ b/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.
--
1.8.4.5
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