From: Josef Bacik <josef@toxicpanda.com>
To: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: reorder extent buffer members for better packing
Date: Thu, 5 Nov 2020 13:12:53 -0500 [thread overview]
Message-ID: <dfebd678-a204-3ec2-9ea0-da49af3aedc0@toxicpanda.com> (raw)
In-Reply-To: <20201103211101.4221-1-dsterba@suse.com>
On 11/3/20 4:11 PM, David Sterba wrote:
> After the rwsem replaced the tree lock implementation, the extent buffer
> got smaller but leaving some holes behind. By changing log_index type
> and reordering, we can squeeze the size further to 240 bytes, measured on
> release config on x86_64. Log_index spans only 3 values and needs to be
> signed.
>
> Before:
>
> struct extent_buffer {
> u64 start; /* 0 8 */
> long unsigned int len; /* 8 8 */
> long unsigned int bflags; /* 16 8 */
> struct btrfs_fs_info * fs_info; /* 24 8 */
> spinlock_t refs_lock; /* 32 4 */
> atomic_t refs; /* 36 4 */
> atomic_t io_pages; /* 40 4 */
> int read_mirror; /* 44 4 */
> struct callback_head callback_head __attribute__((__aligned__(8))); /* 48 16 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> pid_t lock_owner; /* 64 4 */
> bool lock_recursed; /* 68 1 */
>
> /* XXX 3 bytes hole, try to pack */
>
> struct rw_semaphore lock; /* 72 40 */
> short int log_index; /* 112 2 */
>
> /* XXX 6 bytes hole, try to pack */
>
> struct page * pages[16]; /* 120 128 */
>
> /* size: 248, cachelines: 4, members: 14 */
> /* sum members: 239, holes: 2, sum holes: 9 */
> /* forced alignments: 1 */
> /* last cacheline: 56 bytes */
> } __attribute__((__aligned__(8)));
>
> After:
>
> struct extent_buffer {
> u64 start; /* 0 8 */
> long unsigned int len; /* 8 8 */
> long unsigned int bflags; /* 16 8 */
> struct btrfs_fs_info * fs_info; /* 24 8 */
> spinlock_t refs_lock; /* 32 4 */
> atomic_t refs; /* 36 4 */
> atomic_t io_pages; /* 40 4 */
> int read_mirror; /* 44 4 */
> struct callback_head callback_head __attribute__((__aligned__(8))); /* 48 16 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> pid_t lock_owner; /* 64 4 */
> bool lock_recursed; /* 68 1 */
> s8 log_index; /* 69 1 */
>
> /* XXX 2 bytes hole, try to pack */
>
> struct rw_semaphore lock; /* 72 40 */
> struct page * pages[16]; /* 112 128 */
>
> /* size: 240, cachelines: 4, members: 14 */
> /* sum members: 238, holes: 1, sum holes: 2 */
> /* forced alignments: 1 */
> /* last cacheline: 48 bytes */
> } __attribute__((__aligned__(8)));
>
> Signed-off-by: David Sterba <dsterba@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Thanks,
Josef
prev parent reply other threads:[~2020-11-05 18:12 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-03 21:11 [PATCH] btrfs: reorder extent buffer members for better packing David Sterba
2020-11-03 21:25 ` Amy Parker
2020-11-03 23:44 ` Qu Wenruo
2020-11-04 3:55 ` Amy Parker
2020-11-04 15:53 ` David Sterba
2020-11-04 17:42 ` Amy Parker
2020-11-05 18:12 ` Josef Bacik [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=dfebd678-a204-3ec2-9ea0-da49af3aedc0@toxicpanda.com \
--to=josef@toxicpanda.com \
--cc=dsterba@suse.com \
--cc=linux-btrfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox