On Tue, Dec 15 2009 at 10:49pm -0500,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> Eliminate 1 4-byte hole in 'struct dm_io_memory' by moving 'offset'
> above the 'ptr' to which it applies (size reduced from 24 to 16 bytes).
> And by association, 1 4 byte hole is eliminated in 'struct
> dm_io_request' (size reduced from 56 to 48 bytes).
>
> Eliminate all (3 4-byte) holes (and one cache-line) in 'struct
> dm_snapshot' by moving 'pending_pool' after 'pending_exceptions_count'
> and moving 'merge_failed' lower (size reduced from 648 to 632 bytes).
As it happens, I had compiled with CONFIG_DEBUG_SPINLOCK et al. That
explains why dm_snapshot was so large. If I use a "production" .config
I need the following incremental patch to eliminate all 6 4-byte holes
in 'struct dm_snapshot' (reduces size from 392 to 368 bytes):
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 0435442..ab9822e 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -96,6 +96,11 @@ struct dm_snapshot {
*/
spinlock_t pe_lock;
+ /* Chunks with outstanding reads */
+ spinlock_t tracked_chunk_lock;
+ mempool_t *tracked_chunk_pool;
+ struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
+
/* The on disk metadata handler */
struct dm_exception_store *store;
@@ -105,11 +110,6 @@ struct dm_snapshot {
struct bio_list queued_bios;
struct work_struct queued_bios_work;
- /* Chunks with outstanding reads */
- mempool_t *tracked_chunk_pool;
- spinlock_t tracked_chunk_lock;
- struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
-
/* Wait for events based on state_bits */
unsigned long state_bits;
--
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