Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode

From: Amir Goldstein <amir73il@gmail.com>
To: Jeff Layton <jlayton@kernel.org>
Cc: "Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Christian Brauner" <brauner@kernel.org>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"David Sterba" <dsterba@suse.cz>, "Theodore Ts'o" <tytso@mit.edu>,
	"Eric Biederman" <ebiederm@xmission.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Jeremy Kerr" <jk@ozlabs.org>, "Arnd Bergmann" <arnd@arndb.de>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	"Heiko Carstens" <hca@linux.ibm.com>,
	"Vasily Gorbik" <gor@linux.ibm.com>,
	"Alexander Gordeev" <agordeev@linux.ibm.com>,
	"Christian Borntraeger" <borntraeger@linux.ibm.com>,
	"Sven Schnelle" <svens@linux.ibm.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Todd Kjos" <tkjos@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Carlos Llamas" <cmllamas@google.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Mattia Dongili" <malattia@linux.it>,
	"Dennis Dalessandro" <dennis.dalessandro@cornelisnetworks.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Leon Romanovsky" <leon@kernel.org>,
	"Brad Warrum" <bwarrum@linux.ibm.com>,
	"Ritu Agarwal" <rituagar@linux.ibm.com>,
	"Hans de Goede" <hdegoede@redhat.com>,
	"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	"Mark Gross" <markgross@kernel.org>,
	"Jiri Slaby" <jirislaby@kernel.org>,
	"Eric Van Hensbergen" <ericvh@kernel.org>,
	"Latchesar Ionkov" <lucho@ionkov.net>,
	"Dominique Martinet" <asmadeus@codewreck.org>,
	"Christian Schoenebeck" <linux_oss@crudebyte.com>,
	"David Sterba" <dsterba@suse.com>,
	"David Howells" <dhowells@redhat.com>,
	"Marc Dionne" <marc.dionne@auristor.com>,
	"Ian Kent" <raven@themaw.net>,
	"Luis de Bethencourt" <luisbg@kernel.org>,
	"Salah Triki" <salah.triki@gmail.com>,
	"Tigran A. Aivazian" <aivazian.tigran@gmail.com>,
	"Chris Mason" <clm@fb.com>, "Josef Bacik" <josef@toxicpanda.com>,
	"Xiubo Li" <xiubli@redhat.com>,
	"Ilya Dryomov" <idryomov@gmail.com>,
	"Jan Harkes" <jaharkes@cs.cmu.edu>,
	coda@cs.cmu.edu, "Joel Becker" <jlbec@evilplan.org>,
	"Christoph Hellwig" <hch@lst.de>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Gao Xiang" <xiang@kernel.org>, "Chao Yu" <chao@kernel.org>,
	"Yue Hu" <huyue2@coolpad.com>,
	"Jeffle Xu" <jefflexu@linux.alibaba.com>,
	"Namjae Jeon" <linkinjeon@kernel.org>,
	"Sungjong Seo" <sj1557.seo@samsung.com>,
	"Jan Kara" <jack@suse.com>,
	"Andreas Dilger" <adilger.kernel@dilger.ca>,
	"Jaegeuk Kim" <jaegeuk@kernel.org>,
	"OGAWA Hirofumi" <hirofumi@mail.parknet.co.jp>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Miklos Szeredi" <miklos@szeredi.hu>,
	"Bob Peterson" <rpeterso@redhat.com>,
	"Andreas Gruenbacher" <agruenba@redhat.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Anton Ivanov" <anton.ivanov@cambridgegreys.com>,
	"Johannes Berg" <johannes@sipsolutions.net>,
	"Mikulas Patocka" <mikulas@artax.karlin.mff.cuni.cz>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Muchun Song" <muchun.song@linux.dev>, "Jan Kara" <jack@suse.cz>,
	"David Woodhouse" <dwmw2@infradead.org>,
	"Dave Kleikamp" <shaggy@kernel.org>, "Tejun Heo" <tj@kernel.org>,
	"Trond Myklebust" <trond.myklebust@hammerspace.com>,
	"Anna Schumaker" <anna@kernel.org>,
	"Chuck Lever" <chuck.lever@oracle.com>,
	"Neil Brown" <neilb@suse.de>,
	"Olga Kornievskaia" <kolga@netapp.com>,
	"Dai Ngo" <Dai.Ngo@oracle.com>, "Tom Talpey" <tom@talpey.com>,
	"Ryusuke Konishi" <konishi.ryusuke@gmail.com>,
	"Anton Altaparmakov" <anton@tuxera.com>,
	"Konstantin Komarov" <almaz.alexandrovich@paragon-software.com>,
	"Mark Fasheh" <mark@fasheh.com>,
	"Joseph Qi" <joseph.qi@linux.alibaba.com>,
	"Bob Copeland" <me@bobcopeland.com>,
	"Mike Marshall" <hubcap@omnibond.com>,
	"Martin Brandenburg" <martin@omnibond.com>,
	"Luis Chamberlain" <mcgrof@kernel.org>,
	"Iurii Zaikin" <yzaikin@google.com>,
	"Tony Luck" <tony.luck@intel.com>,
	"Guilherme G. Piccoli" <gpiccoli@igalia.com>,
	"Anders Larsen" <al@alarsen.net>,
	"Steve French" <sfrench@samba.org>,
	"Paulo Alcantara" <pc@manguebit.com>,
	"Ronnie Sahlberg" <lsahlber@redhat.com>,
	"Shyam Prasad N" <sprasad@microsoft.com>,
	"Sergey Senozhatsky" <senozhatsky@chromium.org>,
	"Phillip Lougher" <phillip@squashfs.org.uk>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Masami Hiramatsu" <mhiramat@kernel.org>,
	"Evgeniy Dushistov" <dushistov@mail.ru>,
	"Chandan Babu R" <chandan.babu@oracle.com>,
	"Darrick J. Wong" <djwong@kernel.org>,
	"Damien Le Moal" <dlemoal@kernel.org>,
	"Naohiro Aota" <naohiro.aota@wdc.com>,
	"Johannes Thumshirn" <jth@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <martin.lau@linux.dev>,
	"Song Liu" <song@kernel.org>,
	"Yonghong Song" <yonghong.song@linux.dev>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>,
	"Stanislav Fomichev" <sdf@google.com>,
	"Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
	"Hugh Dickins" <hughd@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"John Johansen" <john.johansen@canonical.com>,
	"Paul Moore" <paul@paul-moore.com>,
	"James Morris" <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	"Stephen Smalley" <stephen.smalley.work@gmail.com>,
	"Eric Paris" <eparis@parisplace.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, platform-driver-x86@vger.kernel.org,
	linux-rdma@vger.kernel.org, linux-serial@vger.kernel.org,
	linux-usb@vger.kernel.org, v9fs@lists.linux.dev,
	linux-afs@lists.infradead.org, autofs@vger.kernel.org,
	linux-btrfs@vger.kernel.org, ceph-devel@vger.kernel.org,
	codalist@coda.cs.cmu.edu, linux-efi@vger.kernel.org,
	linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net, gfs2@lists.linux.dev,
	linux-um@lists.infradead.org, linux-mtd@lists.infradead.org,
	jfs-discussion@lists.sourceforge.net, linux-nfs@vger.kernel.org,
	linux-nilfs@vger.kernel.org,
	linux-ntfs-dev@lists.sourceforge.net, ntfs3@lists.linux.dev,
	ocfs2-devel@lists.linux.dev,
	linux-karma-devel@lists.sourceforge.net,
	devel@lists.orangefs.org, linux-unionfs@vger.kernel.org,
	linux-hardening@vger.kernel.org, reiserfs-devel@vger.kernel.org,
	linux-cifs@vger.kernel.org, samba-technical@lists.samba.org,
	linux-trace-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org,
	selinux@vger.kernel.org
Subject: Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode
Date: Thu, 28 Sep 2023 14:35:13 +0300	[thread overview]
Message-ID: <CAOQ4uxjSrgGr+6UOs4ADGYCderpQ7hAaPjNmB1DExAPLQQsHSg@mail.gmail.com> (raw)
In-Reply-To: <20230928110554.34758-3-jlayton@kernel.org>

On Thu, Sep 28, 2023 at 2:06 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> The recent change to use discrete integers instead of struct timespec64
> in struct inode shaved 8 bytes off of it, but it also moves the i_lock
> into the previous cacheline, away from the fields that it protects.
>
> Move i_blocks up above the i_lock, which moves the new 4 byte hole to
> just after the timestamps, without changing the size of the structure.
>

Instead of creating an implicit hole, can you please move i_generation
to fill the 4 bytes hole.

It makes sense in the same cache line with i_ino and I could
use the vacant 4 bytes hole above i_fsnotify_mask to expand the
mask to 64bit (the 32bit event mask space is running out).

Thanks,
Amir.

> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  include/linux/fs.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index de902ff2938b..3e0fe0f52e7c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -677,11 +677,11 @@ struct inode {
>         u32                     i_atime_nsec;
>         u32                     i_mtime_nsec;
>         u32                     i_ctime_nsec;
> +       blkcnt_t                i_blocks;
>         spinlock_t              i_lock; /* i_blocks, i_bytes, maybe i_size */
>         unsigned short          i_bytes;
>         u8                      i_blkbits;
>         u8                      i_write_hint;
> -       blkcnt_t                i_blocks;
>
>  #ifdef __NEED_I_SIZE_ORDERED
>         seqcount_t              i_size_seqcount;
> --
> 2.41.0
>