From: Jan Kara Subject: [PATCH 04/12] fs: Generic infrastructure for optional inode fields Date: Wed, 1 Oct 2014 21:31:26 +0200 Message-ID: <1412191894-9113-5-git-send-email-jack@suse.cz> References: <1412191894-9113-1-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Dave Kleikamp , jfs-discussion@lists.sourceforge.net, tytso@mit.edu, Jeff Mahoney , Mark Fasheh , reiserfs-devel@vger.kernel.org, xfs@oss.sgi.com, cluster-devel@redhat.com, Joel Becker , Jan Kara , linux-ext4@vger.kernel.org, Steven Whitehouse , ocfs2-devel@oss.oracle.com To: linux-fsdevel@vger.kernel.org Return-path: In-Reply-To: <1412191894-9113-1-git-send-email-jack@suse.cz> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com List-Id: linux-ext4.vger.kernel.org There are parts of struct inode which are used only by a few filesystems (e.g. i_dquot pointers, i_mapping->private_list, ...). Thus all the other filesystems are just wasting memory with these fields. On the other hand it isn't simple to just move these fields to filesystem specific part of inode because there is generic code which needs to peek into the fields and it is cumbersome to provide helpers into which fs has to stuff the field it is storing elsewhere. We create a simple infrastructure which allows for optional inode fields stored in the fs-specific part of the inode. Accessing these fields has a slightly worse performance as we have to lookup their offset in the offset table stored in the superblock but in most cases this is acceptable. Notably, this offset-table mechanism is faster than having fs-specific hook functions which would need to be called to provide pointers to desired fields. Signed-off-by: Jan Kara --- include/linux/fs.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/include/linux/fs.h b/include/linux/fs.h index 94187721ad41..977f8fb6ca88 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -615,6 +615,11 @@ struct inode { void *i_private; /* fs or device private pointer */ }; +/* Optional inode fields (stored in filesystems inode if the fs needs them) */ +enum { + IF_FIELD_NR /* Number of optional inode fields */ +}; + static inline int inode_unhashed(struct inode *inode) { return hlist_unhashed(&inode->i_hash); @@ -1236,6 +1241,11 @@ struct super_block { void *s_fs_info; /* Filesystem private info */ unsigned int s_max_links; fmode_t s_mode; + /* + * We could have here just a pointer to the offsets array but this + * way we save one dereference when looking up field offsets + */ + int s_inode_fields[IF_FIELD_NR]; /* Granularity of c/m/atime in ns. Cannot be worse than a second */ @@ -1286,6 +1296,20 @@ struct super_block { struct rcu_head rcu; }; +static inline void *inode_field(const struct inode *inode, int field) +{ + int offset = inode->i_sb->s_inode_fields[field]; + + if (!offset) /* Field not present? */ + return NULL; + return ((char *)inode) + offset; +} + +static inline void sb_init_inode_fields(struct super_block *sb, int *fields) +{ + memcpy(sb->s_inode_fields, fields, sizeof(int) * IF_FIELD_NR); +} + extern struct timespec current_fs_time(struct super_block *sb); /* -- 1.8.1.4 _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs