Hi,
On Thu, 2012-04-05 at 12:11 -0400, Bob Peterson wrote:
> Hi,
>
> Here's another patch (explanation below). This patch replies upon
> a DLM patch that hasn't fully gone upstream yet, so perhaps it
> shouldn't be added to the nmw tree until it is. This greatly
> improves the performance of gfs2_grow in a clustered gfs2 file system.
>
> Regards,
>
I'm still not very keen on dragging in this bit of dlm. If it is really
needed, then we should use the copy in the dlm itself and not add our
own copy of it. Also, why can we not use the GLF_BLOCKING flag for this
purpose? Is there some issue with try locks in that case?
When you say that this relies upon this dlm patch, what does that mean?
What are the consequences of having this patch but not the dlm one? I'm
wondering whether I should hold off on this at least until the dlm one
has been finalised and applied.
Aside from those points though, this is a really big step forward and
should make a measurable difference to performance across the board when
contention between multiple nodes occurs. So I'm very happy to see such
significant progress in this area,
Steve.
> Bob Peterson
> Red Hat File Systems
>
> Signed-off-by: Bob Peterson <rpete...@redhat.com>
> ---
> Author: Bob Peterson <rpete...@redhat.com>
> Date: Wed Apr 4 15:14:51 2012 -0500
>
> GFS2: Instruct DLM to avoid queue convert slowdowns
>
> This patch instructs DLM to prevent an "in place" conversion, where the
> lock just stays on the granted queue, and instead forces the conversion to
> the back of the convert queue. This is done on upward conversions only.
>
> This is useful in cases where, for example, a lock is frequently needed in
> PR on one node, but another node needs it temporarily in EX to update it.
> This may happen, for example, when the rindex is being updated by
> gfs2_grow.
> The gfs2_grow needs to have the lock in EX, but the other nodes need to
> re-read it to retrieve the updates. The glock is already granted in PR on
> the non-growing nodes, so this prevents them from continually re-granting
> the lock in PR, and forces the EX from gfs2_grow to go through.
>
> diff --git a/fs/gfs2/lock_dlm.c b/fs/gfs2/lock_dlm.c
> index bd5af03..43466d6 100644
> --- a/fs/gfs2/lock_dlm.c
> +++ b/fs/gfs2/lock_dlm.c
> @@ -16,6 +16,25 @@
> #include "glock.h"
> #include "util.h"
>
> +/*
> + * Borrowed from dlm's lock.c: We need to only pass the QUECVT bit with
> + * requests that are compatible, so we use dlm's check:
> + *
> + * Compatibility matrix for conversions with QUECVT set.
> + * Granted mode is the row; requested mode is the column.
> + * Usage: matrix[grmode+1][rqmode+1]
> + */
> +static const int quecvt_compat_matrix[8][8] = {
> + /* UN NL CR CW PR PW EX PD */
> + {0, 0, 0, 0, 0, 0, 0, 0}, /* UN */
> + {0, 0, 1, 1, 1, 1, 1, 0}, /* NL */
> + {0, 0, 0, 1, 1, 1, 1, 0}, /* CR */
> + {0, 0, 0, 0, 1, 1, 1, 0}, /* CW */
> + {0, 0, 0, 1, 0, 1, 1, 0}, /* PR */
> + {0, 0, 0, 0, 0, 0, 1, 0}, /* PW */
> + {0, 0, 0, 0, 0, 0, 0, 0}, /* EX */
> + {0, 0, 0, 0, 0, 0, 0, 0} /* PD */
> +};
>
> static void gdlm_ast(void *arg)
> {
> @@ -104,10 +123,13 @@ static int make_mode(const unsigned int lmstate)
> return -1;
> }
>
> -static u32 make_flags(const u32 lkid, const unsigned int gfs_flags,
> +static u32 make_flags(struct gfs2_glock *gl, const unsigned int gfs_flags,
> const int req)
> {
> u32 lkf = 0;
> + u32 lkid = gl->gl_lksb.sb_lkid;
> + int is_upconvert =
> + quecvt_compat_matrix[make_mode(gl->gl_state) + 1][req + 1];
>
> if (gfs_flags & LM_FLAG_TRY)
> lkf |= DLM_LKF_NOQUEUE;
> @@ -131,8 +153,11 @@ static u32 make_flags(const u32 lkid, const unsigned int
> gfs_flags,
> BUG();
> }
>
> - if (lkid != 0)
> + if (lkid != 0) {
> lkf |= DLM_LKF_CONVERT;
> + if (is_upconvert)
> + lkf |= DLM_LKF_QUECVT;
> + }
>
> lkf |= DLM_LKF_VALBLK;
>
> @@ -149,7 +174,7 @@ static unsigned int gdlm_lock(struct gfs2_glock *gl,
>
> gl->gl_req = req_state;
> req = make_mode(req_state);
> - lkf = make_flags(gl->gl_lksb.sb_lkid, flags, req);
> + lkf = make_flags(gl, flags, req);
>
> /*
> * Submit the actual lock request.
>
