[Cluster-devel] [PATCH 2/4] GFS2: Reduce inode size by using 32-bit i_generation

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,

I don't think we can get away with shrinking i_generation. It is 64 bits 
on disk, and in any event the union that you've used for the ondisk 
structures doesn't take into account endianess. We do need to keep all 
64 bits in order to ensure that we never land up with a problem with NFS 
lookups. I guess that you could try and chop it in half, and keep the 
lower bits in the vfs inode and the upper bits in the gfs2 inode, if 
that helps, but I'm not sure that it is worth the effort of doing that 
overall,

Steve.

On 28/10/15 14:20, Bob Peterson wrote:
> This patch removes variable i_generation from gfs2_inode. In its
> place, we use inode->i_generation which is pretty much the same thing,
> in 32-bits. The loss of 32 bits should not be a problem.
>
> Signed-off-by: Bob Peterson <rpeterso@redhat.com>
> ---
>   fs/gfs2/glops.c                  |  2 +-
>   fs/gfs2/incore.h                 |  9 +++++++--
>   fs/gfs2/inode.c                  |  5 +++--
>   fs/gfs2/rgrp.c                   | 16 ++++++++--------
>   fs/gfs2/rgrp.h                   |  2 +-
>   fs/gfs2/super.c                  |  2 +-
>   include/uapi/linux/gfs2_ondisk.h | 25 +++++++++++++++++++++----
>   7 files changed, 42 insertions(+), 19 deletions(-)
>
> diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
> index 1f6c9c3..79cd4a9 100644
> --- a/fs/gfs2/glops.c
> +++ b/fs/gfs2/glops.c
> @@ -358,7 +358,7 @@ static int gfs2_dinode_in(struct gfs2_inode *ip, const void *buf)
>   	ip->i_inode.i_ctime.tv_nsec = be32_to_cpu(str->di_ctime_nsec);
>   
>   	ip->i_goal = be64_to_cpu(str->di_goal_meta);
> -	ip->i_generation = be64_to_cpu(str->di_generation);
> +	ip->i_inode.i_generation = be32_to_cpu(str->di_gen2);
>   
>   	ip->i_diskflags = be32_to_cpu(str->di_flags);
>   	ip->i_eattr = be64_to_cpu(str->di_eattr);
> diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
> index 76c9c77..8ca88b9 100644
> --- a/fs/gfs2/incore.h
> +++ b/fs/gfs2/incore.h
> @@ -88,7 +88,13 @@ struct gfs2_rgrpd {
>   	u32 rd_reserved;                /* number of blocks reserved */
>   	u32 rd_free_clone;
>   	u32 rd_dinodes;
> -	u64 rd_igeneration;
> +	union {
> +		u64 rd_igeneration;
> +		struct {
> +			u32 rd_igen1;
> +			u32 rd_igen2;
> +		};
> +	};
>   	struct gfs2_bitmap *rd_bits;
>   	struct gfs2_sbd *rd_sbd;
>   	struct gfs2_rgrp_lvb *rd_rgl;
> @@ -385,7 +391,6 @@ struct gfs2_inode {
>   	struct inode i_inode;
>   	u64 i_no_addr;
>   	u64 i_no_formal_ino;
> -	u64 i_generation;
>   	u64 i_eattr;
>   	unsigned long i_flags;		/* GIF_... */
>   	struct gfs2_glock *i_gl; /* Move into i_gh? */
> diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
> index 063fdfc..cc815ab 100644
> --- a/fs/gfs2/inode.c
> +++ b/fs/gfs2/inode.c
> @@ -394,8 +394,9 @@ static int alloc_dinode(struct gfs2_inode *ip, u32 flags, unsigned *dblocks)
>   	if (error)
>   		goto out_ipreserv;
>   
> -	error = gfs2_alloc_blocks(ip, &ip->i_no_addr, dblocks, 1, &ip->i_generation);
> -	ip->i_no_formal_ino = ip->i_generation;
> +	error = gfs2_alloc_blocks(ip, &ip->i_no_addr, dblocks, 1,
> +				  &ip->i_inode.i_generation);
> +	ip->i_no_formal_ino = ip->i_inode.i_generation;
>   	ip->i_inode.i_ino = ip->i_no_addr;
>   	ip->i_goal = ip->i_no_addr;
>   
> diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
> index 475985d..34c42a8 100644
> --- a/fs/gfs2/rgrp.c
> +++ b/fs/gfs2/rgrp.c
> @@ -1062,7 +1062,7 @@ static void gfs2_rgrp_in(struct gfs2_rgrpd *rgd, const void *buf)
>   	rgd->rd_flags |= rg_flags;
>   	rgd->rd_free = be32_to_cpu(str->rg_free);
>   	rgd->rd_dinodes = be32_to_cpu(str->rg_dinodes);
> -	rgd->rd_igeneration = be64_to_cpu(str->rg_igeneration);
> +	rgd->rd_igen2 = be32_to_cpu(str->rg_igen2);
>   }
>   
>   static void gfs2_rgrp_out(struct gfs2_rgrpd *rgd, void *buf)
> @@ -1073,7 +1073,7 @@ static void gfs2_rgrp_out(struct gfs2_rgrpd *rgd, void *buf)
>   	str->rg_free = cpu_to_be32(rgd->rd_free);
>   	str->rg_dinodes = cpu_to_be32(rgd->rd_dinodes);
>   	str->__pad = cpu_to_be32(0);
> -	str->rg_igeneration = cpu_to_be64(rgd->rd_igeneration);
> +	str->rg_igen2 = cpu_to_be64(rgd->rd_igen2);
>   	memset(&str->rg_reserved, 0, sizeof(str->rg_reserved));
>   }
>   
> @@ -1084,7 +1084,7 @@ static int gfs2_rgrp_lvb_valid(struct gfs2_rgrpd *rgd)
>   
>   	if (rgl->rl_flags != str->rg_flags || rgl->rl_free != str->rg_free ||
>   	    rgl->rl_dinodes != str->rg_dinodes ||
> -	    rgl->rl_igeneration != str->rg_igeneration)
> +	    rgl->rl_igen2 != str->rg_igen2)
>   		return 0;
>   	return 1;
>   }
> @@ -1097,7 +1097,7 @@ static void gfs2_rgrp_ondisk2lvb(struct gfs2_rgrp_lvb *rgl, const void *buf)
>   	rgl->rl_flags = str->rg_flags;
>   	rgl->rl_free = str->rg_free;
>   	rgl->rl_dinodes = str->rg_dinodes;
> -	rgl->rl_igeneration = str->rg_igeneration;
> +	rgl->rl_igen2 = str->rg_igen2;
>   	rgl->__pad = 0UL;
>   }
>   
> @@ -1229,7 +1229,7 @@ static int update_rgrp_lvb(struct gfs2_rgrpd *rgd)
>   	rgd->rd_free = be32_to_cpu(rgd->rd_rgl->rl_free);
>   	rgd->rd_free_clone = rgd->rd_free;
>   	rgd->rd_dinodes = be32_to_cpu(rgd->rd_rgl->rl_dinodes);
> -	rgd->rd_igeneration = be64_to_cpu(rgd->rd_rgl->rl_igeneration);
> +	rgd->rd_igen2 = be64_to_cpu(rgd->rd_rgl->rl_igen2);
>   	return 0;
>   }
>   
> @@ -2334,7 +2334,7 @@ static void gfs2_set_alloc_start(struct gfs2_rbm *rbm,
>    */
>   
>   int gfs2_alloc_blocks(struct gfs2_inode *ip, u64 *bn, unsigned int *nblocks,
> -		      bool dinode, u64 *generation)
> +		      bool dinode, u32 *generation)
>   {
>   	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
>   	struct buffer_head *dibh;
> @@ -2390,9 +2390,9 @@ int gfs2_alloc_blocks(struct gfs2_inode *ip, u64 *bn, unsigned int *nblocks,
>   	rbm.rgd->rd_free -= *nblocks;
>   	if (dinode) {
>   		rbm.rgd->rd_dinodes++;
> -		*generation = rbm.rgd->rd_igeneration++;
> +		*generation = rbm.rgd->rd_igen2++;
>   		if (*generation == 0)
> -			*generation = rbm.rgd->rd_igeneration++;
> +			*generation = rbm.rgd->rd_igen2++;
>   	}
>   
>   	gfs2_trans_add_meta(rbm.rgd->rd_gl, rbm.rgd->rd_bits[0].bi_bh);
> diff --git a/fs/gfs2/rgrp.h b/fs/gfs2/rgrp.h
> index c0ab33f..71c1a8e 100644
> --- a/fs/gfs2/rgrp.h
> +++ b/fs/gfs2/rgrp.h
> @@ -47,7 +47,7 @@ extern int gfs2_inplace_reserve(struct gfs2_inode *ip,
>   extern void gfs2_inplace_release(struct gfs2_inode *ip);
>   
>   extern int gfs2_alloc_blocks(struct gfs2_inode *ip, u64 *bn, unsigned int *n,
> -			     bool dinode, u64 *generation);
> +			     bool dinode, u32 *generation);
>   
>   extern int gfs2_rs_alloc(struct gfs2_inode *ip);
>   extern void gfs2_rs_deltree(struct gfs2_blkreserv *rs);
> diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
> index 894fb01..928be2f 100644
> --- a/fs/gfs2/super.c
> +++ b/fs/gfs2/super.c
> @@ -714,7 +714,7 @@ void gfs2_dinode_out(const struct gfs2_inode *ip, void *buf)
>   
>   	str->di_goal_meta = cpu_to_be64(ip->i_goal);
>   	str->di_goal_data = cpu_to_be64(ip->i_goal);
> -	str->di_generation = cpu_to_be64(ip->i_generation);
> +	str->di_gen2 = cpu_to_be64(ip->i_inode.i_generation);
>   
>   	str->di_flags = cpu_to_be32(ip->i_diskflags);
>   	str->di_height = cpu_to_be16(ip->i_height);
> diff --git a/include/uapi/linux/gfs2_ondisk.h b/include/uapi/linux/gfs2_ondisk.h
> index 1a763ea..bef244e 100644
> --- a/include/uapi/linux/gfs2_ondisk.h
> +++ b/include/uapi/linux/gfs2_ondisk.h
> @@ -175,7 +175,13 @@ struct gfs2_rgrp_lvb {
>   	__be32 rl_flags;
>   	__be32 rl_free;
>   	__be32 rl_dinodes;
> -	__be64 rl_igeneration;
> +	union {
> +		__be64 rl_igeneration;
> +		struct {
> +			__be32 rl_igen1;
> +			__be32 rl_igen2;
> +		};
> +	};
>   	__be32 rl_unlinked;
>   	__be32 __pad;
>   };
> @@ -187,7 +193,13 @@ struct gfs2_rgrp {
>   	__be32 rg_free;
>   	__be32 rg_dinodes;
>   	__be32 __pad;
> -	__be64 rg_igeneration;
> +	union {
> +		__be64 rg_igeneration;
> +		struct {
> +			__be32 rg_igen1;
> +			__be32 rg_igen2;
> +		};
> +	};
>   
>   	__u8 rg_reserved[80]; /* Several fields from gfs1 now reserved */
>   };
> @@ -268,8 +280,13 @@ struct gfs2_dinode {
>   	 */
>   	__be64 di_goal_meta;	/* rgrp to alloc from next */
>   	__be64 di_goal_data;	/* data block goal */
> -	__be64 di_generation;	/* generation number for NFS */
> -
> +	union {
> +		__be64 di_generation;	/* generation number for NFS */
> +		struct {
> +			__be32 di_gen1;
> +			__be32 di_gen2;
> +		};
> +	};
>   	__be32 di_flags;	/* GFS2_DIF_... */
>   	__be32 di_payload_format;  /* GFS2_FORMAT_... */
>   	__u16 __pad1;	/* Was ditype in gfs1 */