As Ted noted, the ext4_allocation_request isn't well aligned.
Looking at it with pahole we're wasting space on 64-bit
arches:
struct ext4_allocation_request {
struct inode * inode; /* 0 8 */
ext4_lblk_t logical; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
ext4_fsblk_t goal; /* 16 8 */
ext4_lblk_t lleft; /* 24 4 */
/* XXX 4 bytes hole, try to pack */
ext4_fsblk_t pleft; /* 32 8 */
ext4_lblk_t lright; /* 40 4 */
/* XXX 4 bytes hole, try to pack */
ext4_fsblk_t pright; /* 48 8 */
unsigned int len; /* 56 4 */
unsigned int flags; /* 60 4 */
/* --- cacheline 1 boundary (64 bytes) --- */
/* size: 64, cachelines: 1, members: 9 */
/* sum members: 52, holes: 3, sum holes: 12 */
};
grouping 32-bit members together closes these holes and shrinks
the structure by 12 bytes.
Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---
V2: fix comments, thanks to Mike Snitzer
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cc7d5ed..cefd94a 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -93,20 +93,20 @@ typedef unsigned int ext4_group_t;
struct ext4_allocation_request {
/* target inode for block we're allocating */
struct inode *inode;
+ /* how many blocks we want to allocate */
+ unsigned int len;
/* logical block in target inode */
ext4_lblk_t logical;
- /* phys. target (a hint) */
- ext4_fsblk_t goal;
/* the closest logical allocated block to the left */
ext4_lblk_t lleft;
- /* phys. block for ^^^ */
- ext4_fsblk_t pleft;
/* the closest logical allocated block to the right */
ext4_lblk_t lright;
- /* phys. block for ^^^ */
+ /* phys. target (a hint) */
+ ext4_fsblk_t goal;
+ /* phys. block for the closest logical allocated block to the left */
+ ext4_fsblk_t pleft;
+ /* phys. block for the closest logical allocated block to the right */
ext4_fsblk_t pright;
- /* how many blocks we want to allocate */
- unsigned int len;
/* flags. see above EXT4_MB_HINT_* */
unsigned int flags;
};
--
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