[Cluster-devel] [PATCH 1/2] GFS2: Introduce GLF_EX_SHARING bit: local EX sharing

[Andreas Gruenbacher <agruenba@redhat.com>]

On 8 May 2018 at 22:04, Bob Peterson <rpeterso@redhat.com> wrote:
> This patch is a first step in rgrp sharing. It allows for glocks
> locked in EX mode to be shared amongst processes on that node.
> Like a Shared glock, multiple processes may hold the lock in
> EX mode at the same time, provided they're all on the same
> node. All other nodes will see this as an EX lock.
> For now, there are no users of the new flag. A future patch
> will use it to improve performance with rgrp sharing.

The flag isn't called GLF_EX_SHARING anymore, so please fix the
subject. I don't like the flag name LM_FLAG_SHAREDEX very much. The
flag indicates that the node holds a glock exclusively and individual
processes on the node can share it, so how about LM_FLAG_NODEEX or
similar instead?

> Signed-off-by: Bob Peterson <rpeterso@redhat.com>
> ---
>  fs/gfs2/glock.c | 23 +++++++++++++++++++----
>  fs/gfs2/glock.h |  4 ++++
>  2 files changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
> index 097bd3c0f270..a463de5fad2e 100644
> --- a/fs/gfs2/glock.c
> +++ b/fs/gfs2/glock.c
> @@ -279,10 +279,20 @@ void gfs2_glock_put(struct gfs2_glock *gl)
>
>  static inline int may_grant(const struct gfs2_glock *gl, const struct gfs2_holder *gh)
>  {
> -       const struct gfs2_holder *gh_head = list_entry(gl->gl_holders.next, const struct gfs2_holder, gh_list);
> -       if ((gh->gh_state == LM_ST_EXCLUSIVE ||
> -            gh_head->gh_state == LM_ST_EXCLUSIVE) && gh != gh_head)
> -               return 0;
> +       const struct gfs2_holder *gh_head = list_entry(gl->gl_holders.next,
> +                                                      const struct gfs2_holder,
> +                                                      gh_list);
> +
> +       if (gh != gh_head) {
> +               if (gh_head->gh_state == LM_ST_EXCLUSIVE &&
> +                   (gh_head->gh_flags & LM_FLAG_SHAREDEX) &&
> +                   gh->gh_state == LM_ST_EXCLUSIVE &&
> +                   (gh->gh_flags & LM_FLAG_SHAREDEX))
> +                       return 1;
> +               if ((gh->gh_state == LM_ST_EXCLUSIVE ||
> +                    gh_head->gh_state == LM_ST_EXCLUSIVE))
> +                       return 0;
> +       }
>         if (gl->gl_state == gh->gh_state)
>                 return 1;
>         if (gh->gh_flags & GL_EXACT)
> @@ -292,6 +302,9 @@ static inline int may_grant(const struct gfs2_glock *gl, const struct gfs2_holde
>                         return 1;
>                 if (gh->gh_state == LM_ST_DEFERRED && gh_head->gh_state == LM_ST_DEFERRED)
>                         return 1;
> +               if (gh_head->gh_flags & LM_FLAG_SHAREDEX &&
> +                   gh->gh_flags & LM_FLAG_SHAREDEX)
> +                       return 1;
>         }
>         if (gl->gl_state != LM_ST_UNLOCKED && (gh->gh_flags & LM_FLAG_ANY))
>                 return 1;
> @@ -1680,6 +1693,8 @@ static const char *hflags2str(char *buf, u16 flags, unsigned long iflags)
>                 *p++ = 'A';
>         if (flags & LM_FLAG_PRIORITY)
>                 *p++ = 'p';
> +       if (flags & LM_FLAG_SHAREDEX)
> +               *p++ = 's';
>         if (flags & GL_ASYNC)
>                 *p++ = 'a';
>         if (flags & GL_EXACT)
> diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
> index 5e12220cc0c2..3ab7d7f8d986 100644
> --- a/fs/gfs2/glock.h
> +++ b/fs/gfs2/glock.h
> @@ -78,6 +78,9 @@ enum {
>   * request and directly join the other shared lock.  A shared lock request
>   * without the priority flag might be forced to wait until the deferred
>   * requested had acquired and released the lock.
> + *
> + * LM_FLAG_SHAREDEX
> + * The glock may be held in EXCLUSIVE mode, but it's still shared

That doesn't work to document what the flag does, sorry.

>   */
>
>  #define LM_FLAG_TRY            0x0001
> @@ -85,6 +88,7 @@ enum {
>  #define LM_FLAG_NOEXP          0x0004
>  #define LM_FLAG_ANY            0x0008
>  #define LM_FLAG_PRIORITY       0x0010
> +#define LM_FLAG_SHAREDEX       0x0020
>  #define GL_ASYNC               0x0040
>  #define GL_EXACT               0x0080
>  #define GL_SKIP                        0x0100
> --
> 2.14.3
>

Thanks,
Andreas