Re: [f2fs-dev] [PATCH v2] f2fs: merge two uchar variable in struct node_info to reduce memory cost

[Changman Lee]

Hi Yu,

This patch is effective only in 32 bit machine. In case of 64 bit
machine, nat_entry will be aligned in 8 bytes due to pointer variable
(i.e. struct list_head). So it can't get any benefit to reduce memory
usage. In the case of node_info, however, it will be gain in terms of
memory usage.
Hence, I think it's not correct for commit log to describe this patch.

Thanks,

Reviewed-by: Changman Lee <cm224.lee@xxxxxxxxxxx>

2014-12-15 18:33 GMT+09:00 Chao Yu <chao2.yu@xxxxxxxxxxx>:
> This patch moves one member of struct nat_entry: _flag_ to struct node_info,
> so _version_ in struct node_info and _flag_ with unsigned char type will merge
> to one 32-bit space in register/memory. Then the size of nat_entry will reduce
> its size from 28 bytes to 24 bytes and slab memory using by f2fs will be
> reduced.
>
> changes from v1:
>  o introduce inline copy_node_info() to copy valid data from node info suggested
>    by Jaegeuk Kim, it can avoid bug.
>
> Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
> ---
>  fs/f2fs/node.c |  4 ++--
>  fs/f2fs/node.h | 33 ++++++++++++++++++++++-----------
>  2 files changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index f83326c..5aa54a0 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -268,7 +268,7 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
>         e = __lookup_nat_cache(nm_i, ni->nid);
>         if (!e) {
>                 e = grab_nat_entry(nm_i, ni->nid);
> -               e->ni = *ni;
> +               copy_node_info(&e->ni, ni);
>                 f2fs_bug_on(sbi, ni->blk_addr == NEW_ADDR);
>         } else if (new_blkaddr == NEW_ADDR) {
>                 /*
> @@ -276,7 +276,7 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
>                  * previous nat entry can be remained in nat cache.
>                  * So, reinitialize it with new information.
>                  */
> -               e->ni = *ni;
> +               copy_node_info(&e->ni, ni);
>                 f2fs_bug_on(sbi, ni->blk_addr != NULL_ADDR);
>         }
>
> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> index d10b644..eb59167 100644
> --- a/fs/f2fs/node.h
> +++ b/fs/f2fs/node.h
> @@ -29,6 +29,14 @@
>  /* return value for read_node_page */
>  #define LOCKED_PAGE    1
>
> +/* For flag in struct node_info */
> +enum {
> +       IS_CHECKPOINTED,        /* is it checkpointed before? */
> +       HAS_FSYNCED_INODE,      /* is the inode fsynced before? */
> +       HAS_LAST_FSYNC,         /* has the latest node fsync mark? */
> +       IS_DIRTY,               /* this nat entry is dirty? */
> +};
> +
>  /*
>   * For node information
>   */
> @@ -37,18 +45,11 @@ struct node_info {
>         nid_t ino;              /* inode number of the node's owner */
>         block_t blk_addr;       /* block address of the node */
>         unsigned char version;  /* version of the node */
> -};
> -
> -enum {
> -       IS_CHECKPOINTED,        /* is it checkpointed before? */
> -       HAS_FSYNCED_INODE,      /* is the inode fsynced before? */
> -       HAS_LAST_FSYNC,         /* has the latest node fsync mark? */
> -       IS_DIRTY,               /* this nat entry is dirty? */
> +       unsigned char flag;     /* for node information bits */
>  };
>
>  struct nat_entry {
>         struct list_head list;  /* for clean or dirty nat list */
> -       unsigned char flag;     /* for node information bits */
>         struct node_info ni;    /* in-memory node information */
>  };
>
> @@ -63,20 +64,30 @@ struct nat_entry {
>
>  #define inc_node_version(version)      (++version)
>
> +static inline void copy_node_info(struct node_info *dst,
> +                                               struct node_info *src)
> +{
> +       dst->nid = src->nid;
> +       dst->ino = src->ino;
> +       dst->blk_addr = src->blk_addr;
> +       dst->version = src->version;
> +       /* should not copy flag here */
> +}
> +
>  static inline void set_nat_flag(struct nat_entry *ne,
>                                 unsigned int type, bool set)
>  {
>         unsigned char mask = 0x01 << type;
>         if (set)
> -               ne->flag |= mask;
> +               ne->ni.flag |= mask;
>         else
> -               ne->flag &= ~mask;
> +               ne->ni.flag &= ~mask;
>  }
>
>  static inline bool get_nat_flag(struct nat_entry *ne, unsigned int type)
>  {
>         unsigned char mask = 0x01 << type;
> -       return ne->flag & mask;
> +       return ne->ni.flag & mask;
>  }
>
>  static inline void nat_reset_flag(struct nat_entry *ne)
> --
> 2.1.2
>
>
>
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