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authorEric Sandeen <sandeen@redhat.com>2009-07-13 10:24:17 -0400
committerTheodore Ts'o <tytso@mit.edu>2009-07-13 10:24:17 -0400
commit726447d803802cd0be8f62d17c4a34421781b938 (patch)
treeef1d7d4b9afb0f81b9eb6f09980c152d35ceb3cf /fs/ext4
parent089ceecc1ea4a69ed8bcc5c7c7b96ce487e26b33 (diff)
ext4: naturally align struct ext4_allocation_request
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. which is important since ext4 can get on the hairy edge of stack overruns. Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'fs/ext4')
-rw-r--r--fs/ext4/ext4.h14
1 files changed, 7 insertions, 7 deletions
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0ddf7e55abe..9714db393ef 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;
};