From 282ab3ff16120ec670fe3330e85f8ebf13092f21 Mon Sep 17 00:00:00 2001 From: David Sterba Date: Mon, 14 Oct 2019 14:38:33 +0200 Subject: btrfs: reduce compressed_bio members' types Several members of compressed_bio are of type that's unnecessarily big for the values that they'd hold: - the size of the uncompressed and compressed data is 128K now, we can keep is as int - same for number of pages - the compress type fits to a byte - the errors is 0/1 The size of the unpatched structure is 80 bytes with several holes. Reordering nr_pages next to the pages the hole after pending_bios is filled and the resulting size is 56 bytes. This keeps the csums array aligned to 8 bytes, which is nice. Further size optimizations may be possible but right now it looks good to me: struct compressed_bio { refcount_t pending_bios; /* 0 4 */ unsigned int nr_pages; /* 4 4 */ struct page * * compressed_pages; /* 8 8 */ struct inode * inode; /* 16 8 */ u64 start; /* 24 8 */ unsigned int len; /* 32 4 */ unsigned int compressed_len; /* 36 4 */ u8 compress_type; /* 40 1 */ u8 errors; /* 41 1 */ /* XXX 2 bytes hole, try to pack */ int mirror_num; /* 44 4 */ struct bio * orig_bio; /* 48 8 */ u8 sums[]; /* 56 0 */ /* size: 56, cachelines: 1, members: 12 */ /* sum members: 54, holes: 1, sum holes: 2 */ /* last cacheline: 56 bytes */ }; Reviewed-by: Anand Jain Signed-off-by: David Sterba --- fs/btrfs/compression.h | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) (limited to 'fs/btrfs/compression.h') diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h index 8001b700ea3a..00d8439048c9 100644 --- a/fs/btrfs/compression.h +++ b/fs/btrfs/compression.h @@ -31,6 +31,9 @@ struct compressed_bio { /* number of bios pending for this compressed extent */ refcount_t pending_bios; + /* Number of compressed pages in the array */ + unsigned int nr_pages; + /* the pages with the compressed data on them */ struct page **compressed_pages; @@ -40,20 +43,17 @@ struct compressed_bio { /* starting offset in the inode for our pages */ u64 start; - /* number of bytes in the inode we're working on */ - unsigned long len; - - /* number of bytes on disk */ - unsigned long compressed_len; + /* Number of bytes in the inode we're working on */ + unsigned int len; - /* the compression algorithm for this bio */ - int compress_type; + /* Number of bytes on disk */ + unsigned int compressed_len; - /* number of compressed pages in the array */ - unsigned long nr_pages; + /* The compression algorithm for this bio */ + u8 compress_type; /* IO errors */ - int errors; + u8 errors; int mirror_num; /* for reads, this is the bio we are copying the data into */ -- cgit v1.2.3