Re: [PATCH 6/9] btrfs: reduce compressed_bio members' types
From: Anand Jain <hidden>
Date: 2021-05-26 08:41:52
On 26/05/2021 01:08, David Sterba wrote:
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 */
};
The following member types of struct compressed_bio are changed here:
- unsigned long len;
+ unsigned int len;
- int compress_type;
+ u8 compress_type;
- unsigned long nr_pages;
+ unsigned int nr_pages;
- unsigned long compressed_len;
+ unsigned int compressed_len;
- int errors;
+ u8 errors;
There are no warnings.
But in btrfs_submit_compressed_write()
Essentially struct compressed_bio is updated from struct async_extent.
struct async_extent {
u64 start;
u64 ram_size;
u64 compressed_size;
struct page **pages;
unsigned long nr_pages;
int compress_type;
struct list_head list;
};
which can be looked into later.
For now, with the patch
btrfs: optimize users of members of the struct compressed_bio
which is sent to ML.
Reviewed-by: Anand Jain <redacted>
quoted hunk ↗ jump to hunk
Signed-off-by: David Sterba <dsterba@suse.com> --- fs/btrfs/compression.c | 2 +- fs/btrfs/compression.h | 20 ++++++++++---------- 2 files changed, 11 insertions(+), 11 deletions(-)diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index 9a0c26e4e389..c006f5d81c2a 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c@@ -507,7 +507,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start, } if (bytes_left < PAGE_SIZE) { btrfs_info(fs_info, - "bytes left %lu compress len %lu nr %lu", + "bytes left %lu compress len %u nr %u", bytes_left, cb->compressed_len, cb->nr_pages); } bytes_left -= PAGE_SIZE;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 */