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Re: [Cluster-devel] [PATCH] [GFS2] bz253768 (bz248480 try 2) delay glock demote for a minimum hold time



Hi,

Now in the -nmw git tree. Thanks,

Steve.

On Thu, 2007-08-23 at 13:19 -0500, Benjamin Marzinski wrote:
> When a lot of IO, with some distributed mmap IO, is run on a GFS2 filesystem in
> a cluster, it will deadlock. The reason is that do_no_page() will repeatedly
> call gfs2_sharewrite_nopage(), because each node keeps giving up the glock
> too early, and is forced to call unmap_mapping_range(). This bumps the
> mapping->truncate_count sequence count, forcing do_no_page() to retry. This
> patch institutes a minimum glock hold time a tenth a second.  This insures
> that even in heavy contention cases, the node has enough time to get some
> useful work done before it gives up the glock.
> 
> A second issue is that when gfs2_glock_dq() is called from within a page fault
> to demote a lock, and the associated page needs to be written out, it will
> try to acqire a lock on it, but it has already been locked at a higher level.
> This patch puts makes gfs2_glock_dq() use the work queue as well, to avoid this
> issue. This is the same patch as Steve Whitehouse originally proposed to fix
> this issue, execpt that gfs2_glock_dq() now grabs a reference to the glock
> before it queues up the work on it.
> 
> This still doesn't allow the tests to complete. However the remaining bug is a
> known one that will be fixed once Nick Piggin's VFS interface changes have gone
> in.
> 
> Signed-off-by: Benjamin E. Marzinski <bmarzins redhat com>
> 
> plain text document attachment (add-glock-workqueue.patch)
> diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
> index 3d94918..021237d 100644
> --- a/fs/gfs2/glock.c
> +++ b/fs/gfs2/glock.c
> @@ -27,6 +27,8 @@
>  #include <linux/debugfs.h>
>  #include <linux/kthread.h>
>  #include <linux/freezer.h>
> +#include <linux/workqueue.h>
> +#include <linux/jiffies.h>
>  
>  #include "gfs2.h"
>  #include "incore.h"
> @@ -58,10 +60,13 @@
>  static int dump_glock(struct glock_iter *gi, struct gfs2_glock *gl);
>  static void gfs2_glock_xmote_th(struct gfs2_glock *gl, struct gfs2_holder *gh);
>  static void gfs2_glock_drop_th(struct gfs2_glock *gl);
> +static void run_queue(struct gfs2_glock *gl);
> +
>  static DECLARE_RWSEM(gfs2_umount_flush_sem);
>  static struct dentry *gfs2_root;
>  static struct task_struct *scand_process;
>  static unsigned int scand_secs = 5;
> +static struct workqueue_struct *glock_workqueue;
>  
>  #define GFS2_GL_HASH_SHIFT      15
>  #define GFS2_GL_HASH_SIZE       (1 << GFS2_GL_HASH_SHIFT)
> @@ -277,6 +282,18 @@
>  	return gl;
>  }
>  
> +static void glock_work_func(struct work_struct *work)
> +{
> +	struct gfs2_glock *gl = container_of(work, struct gfs2_glock, gl_work.work);
> +
> +	spin_lock(&gl->gl_spin);
> +	if (test_and_clear_bit(GLF_PENDING_DEMOTE, &gl->gl_flags))
> +		set_bit(GLF_DEMOTE, &gl->gl_flags);
> +	run_queue(gl);
> +	spin_unlock(&gl->gl_spin);
> +	gfs2_glock_put(gl);
> +}
> +
>  /**
>   * gfs2_glock_get() - Get a glock, or create one if one doesn't exist
>   * @sdp: The GFS2 superblock
> @@ -316,6 +333,7 @@
>  	gl->gl_name = name;
>  	atomic_set(&gl->gl_ref, 1);
>  	gl->gl_state = LM_ST_UNLOCKED;
> +	gl->gl_demote_state = LM_ST_EXCLUSIVE;
>  	gl->gl_hash = hash;
>  	gl->gl_owner_pid = 0;
>  	gl->gl_ip = 0;
> @@ -324,10 +342,12 @@
>  	gl->gl_req_bh = NULL;
>  	gl->gl_vn = 0;
>  	gl->gl_stamp = jiffies;
> +	gl->gl_tchange = jiffies;
>  	gl->gl_object = NULL;
>  	gl->gl_sbd = sdp;
>  	gl->gl_aspace = NULL;
>  	lops_init_le(&gl->gl_le, &gfs2_glock_lops);
> +	INIT_DELAYED_WORK(&gl->gl_work, glock_work_func);
>  
>  	/* If this glock protects actual on-disk data or metadata blocks,
>  	   create a VFS inode to manage the pages/buffers holding them. */
> @@ -441,6 +461,8 @@
>  
>  static void gfs2_demote_wake(struct gfs2_glock *gl)
>  {
> +	BUG_ON(!spin_is_locked(&gl->gl_spin));
> +	gl->gl_demote_state = LM_ST_EXCLUSIVE;
>          clear_bit(GLF_DEMOTE, &gl->gl_flags);
>          smp_mb__after_clear_bit();
>          wake_up_bit(&gl->gl_flags, GLF_DEMOTE);
> @@ -682,10 +704,14 @@
>   * practise: LM_ST_SHARED and LM_ST_UNLOCKED
>   */
>  
> -static void handle_callback(struct gfs2_glock *gl, unsigned int state, int remote)
> +static void handle_callback(struct gfs2_glock *gl, unsigned int state,
> +			    int remote, unsigned long delay)
>  {
> +	int bit = delay ? GLF_PENDING_DEMOTE : GLF_DEMOTE;
> +
>  	spin_lock(&gl->gl_spin);
> -	if (test_and_set_bit(GLF_DEMOTE, &gl->gl_flags) == 0) {
> +	set_bit(bit, &gl->gl_flags);
> +	if (gl->gl_demote_state == LM_ST_EXCLUSIVE) {
>  		gl->gl_demote_state = state;
>  		gl->gl_demote_time = jiffies;
>  		if (remote && gl->gl_ops->go_type == LM_TYPE_IOPEN &&
> @@ -727,6 +753,7 @@
>  	}
>  
>  	gl->gl_state = new_state;
> +	gl->gl_tchange = jiffies;
>  }
>  
>  /**
> @@ -813,7 +840,6 @@
>  		gl->gl_req_gh = NULL;
>  		gl->gl_req_bh = NULL;
>  		clear_bit(GLF_LOCK, &gl->gl_flags);
> -		run_queue(gl);
>  		spin_unlock(&gl->gl_spin);
>  	}
>  
> @@ -885,7 +911,6 @@
>  	gfs2_assert_warn(sdp, !ret);
>  
>  	state_change(gl, LM_ST_UNLOCKED);
> -	gfs2_demote_wake(gl);
>  
>  	if (glops->go_inval)
>  		glops->go_inval(gl, DIO_METADATA);
> @@ -898,10 +923,10 @@
>  	}
>  
>  	spin_lock(&gl->gl_spin);
> +	gfs2_demote_wake(gl);
>  	gl->gl_req_gh = NULL;
>  	gl->gl_req_bh = NULL;
>  	clear_bit(GLF_LOCK, &gl->gl_flags);
> -	run_queue(gl);
>  	spin_unlock(&gl->gl_spin);
>  
>  	gfs2_glock_put(gl);
> @@ -1209,9 +1234,10 @@
>  {
>  	struct gfs2_glock *gl = gh->gh_gl;
>  	const struct gfs2_glock_operations *glops = gl->gl_ops;
> +	unsigned delay = 0;
>  
>  	if (gh->gh_flags & GL_NOCACHE)
> -		handle_callback(gl, LM_ST_UNLOCKED, 0);
> +		handle_callback(gl, LM_ST_UNLOCKED, 0, 0);
>  
>  	gfs2_glmutex_lock(gl);
>  
> @@ -1229,8 +1255,14 @@
>  	}
>  
>  	clear_bit(GLF_LOCK, &gl->gl_flags);
> -	run_queue(gl);
>  	spin_unlock(&gl->gl_spin);
> +
> +	gfs2_glock_hold(gl);
> +	if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
> +	    !test_bit(GLF_DEMOTE, &gl->gl_flags))
> +		delay = gl->gl_ops->go_min_hold_time;
> +	if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
> +		gfs2_glock_put(gl);
>  }
>  
>  void gfs2_glock_dq_wait(struct gfs2_holder *gh)
> @@ -1457,18 +1489,21 @@
>  			unsigned int state)
>  {
>  	struct gfs2_glock *gl;
> +	unsigned long delay = 0;
> +	unsigned long holdtime;
> +	unsigned long now = jiffies;
>  
>  	gl = gfs2_glock_find(sdp, name);
>  	if (!gl)
>  		return;
>  
> -	handle_callback(gl, state, 1);
> -
> -	spin_lock(&gl->gl_spin);
> -	run_queue(gl);
> -	spin_unlock(&gl->gl_spin);
> +	holdtime = gl->gl_tchange + gl->gl_ops->go_min_hold_time;
> +	if (time_before(now, holdtime))
> +		delay = holdtime - now;
>  
> -	gfs2_glock_put(gl);
> +	handle_callback(gl, state, 1, delay);
> +	if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
> +		gfs2_glock_put(gl);
>  }
>  
>  /**
> @@ -1509,7 +1544,8 @@
>  			return;
>  		if (!gfs2_assert_warn(sdp, gl->gl_req_bh))
>  			gl->gl_req_bh(gl, async->lc_ret);
> -		gfs2_glock_put(gl);
> +		if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
> +			gfs2_glock_put(gl);
>  		up_read(&gfs2_umount_flush_sem);
>  		return;
>  	}
> @@ -1602,7 +1638,7 @@
>  	if (gfs2_glmutex_trylock(gl)) {
>  		if (list_empty(&gl->gl_holders) &&
>  		    gl->gl_state != LM_ST_UNLOCKED && demote_ok(gl))
> -			handle_callback(gl, LM_ST_UNLOCKED, 0);
> +			handle_callback(gl, LM_ST_UNLOCKED, 0, 0);
>  		gfs2_glmutex_unlock(gl);
>  	}
>  
> @@ -1702,7 +1738,7 @@
>  	if (gfs2_glmutex_trylock(gl)) {
>  		if (list_empty(&gl->gl_holders) &&
>  		    gl->gl_state != LM_ST_UNLOCKED)
> -			handle_callback(gl, LM_ST_UNLOCKED, 0);
> +			handle_callback(gl, LM_ST_UNLOCKED, 0, 0);
>  		gfs2_glmutex_unlock(gl);
>  	}
>  }
> @@ -2009,11 +2045,18 @@
>  	if (IS_ERR(scand_process))
>  		return PTR_ERR(scand_process);
>  
> +	glock_workqueue = create_workqueue("glock_workqueue");
> +	if (IS_ERR(glock_workqueue)) {
> +		kthread_stop(scand_process);
> +		return PTR_ERR(glock_workqueue);
> +	}
> +
>  	return 0;
>  }
>  
>  void gfs2_glock_exit(void)
>  {
> +	destroy_workqueue(glock_workqueue);
>  	kthread_stop(scand_process);
>  }
>  
> diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
> --- a/fs/gfs2/glops.c
> +++ b/fs/gfs2/glops.c
> @@ -454,6 +454,7 @@
>  	.go_lock = inode_go_lock,
>  	.go_unlock = inode_go_unlock,
>  	.go_type = LM_TYPE_INODE,
> +	.go_min_hold_time = HZ / 10,
>  };
>  
>  const struct gfs2_glock_operations gfs2_rgrp_glops = {
> @@ -464,6 +465,7 @@
>  	.go_lock = rgrp_go_lock,
>  	.go_unlock = rgrp_go_unlock,
>  	.go_type = LM_TYPE_RGRP,
> +	.go_min_hold_time = HZ / 10,
>  };
>  
>  const struct gfs2_glock_operations gfs2_trans_glops = {
> diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
> --- a/fs/gfs2/incore.h
> +++ b/fs/gfs2/incore.h
> @@ -11,6 +11,7 @@
>  #define __INCORE_DOT_H__
>  
>  #include <linux/fs.h>
> +#include <linux/workqueue.h>
>  
>  #define DIO_WAIT	0x00000010
>  #define DIO_METADATA	0x00000020
> @@ -130,6 +131,7 @@
>  	int (*go_lock) (struct gfs2_holder *gh);
>  	void (*go_unlock) (struct gfs2_holder *gh);
>  	const int go_type;
> +	const unsigned long go_min_hold_time;
>  };
>  
>  enum {
> @@ -161,6 +163,7 @@
>  	GLF_LOCK		= 1,
>  	GLF_STICKY		= 2,
>  	GLF_DEMOTE		= 3,
> +	GLF_PENDING_DEMOTE	= 4,
>  	GLF_DIRTY		= 5,
>  };
>  
> @@ -193,6 +196,7 @@
>  
>  	u64 gl_vn;
>  	unsigned long gl_stamp;
> +	unsigned long gl_tchange;
>  	void *gl_object;
>  
>  	struct list_head gl_reclaim;
> @@ -203,6 +207,7 @@
>  	struct gfs2_log_element gl_le;
>  	struct list_head gl_ail_list;
>  	atomic_t gl_ail_count;
> +	struct delayed_work gl_work;
>  };
>  
>  struct gfs2_alloc {


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