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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>
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1 changed files with 12 additions and 12 deletions
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@ -93,20 +93,20 @@ typedef unsigned int ext4_group_t;
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struct ext4_allocation_request {
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struct ext4_allocation_request {
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/* target inode for block we're allocating */
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/* target inode for block we're allocating */
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struct inode *inode;
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struct inode *inode;
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/* logical block in target inode */
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ext4_lblk_t logical;
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/* phys. target (a hint) */
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ext4_fsblk_t goal;
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/* the closest logical allocated block to the left */
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ext4_lblk_t lleft;
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/* phys. block for ^^^ */
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ext4_fsblk_t pleft;
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/* the closest logical allocated block to the right */
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ext4_lblk_t lright;
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/* phys. block for ^^^ */
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ext4_fsblk_t pright;
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/* how many blocks we want to allocate */
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/* how many blocks we want to allocate */
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unsigned int len;
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unsigned int len;
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/* logical block in target inode */
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ext4_lblk_t logical;
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/* the closest logical allocated block to the left */
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ext4_lblk_t lleft;
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/* the closest logical allocated block to the right */
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ext4_lblk_t lright;
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/* phys. target (a hint) */
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ext4_fsblk_t goal;
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/* phys. block for the closest logical allocated block to the left */
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ext4_fsblk_t pleft;
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/* phys. block for the closest logical allocated block to the right */
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ext4_fsblk_t pright;
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/* flags. see above EXT4_MB_HINT_* */
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/* flags. see above EXT4_MB_HINT_* */
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unsigned int flags;
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unsigned int flags;
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};
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};
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