[PATCH 30/51] [GFS2] delay glock demote for a minimum hold time

swhiteho
2007-10-04T09:29:04Z

From: Benjamin Marzinski <bmarzins@redhat.com>

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.

Signed-off-by: Benjamin E. Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 3d94918..931368a 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 gfs2_dump_lockstate(struct gfs2_sbd *sdp);
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 @@ static struct gfs2_glock *gfs2_glock_find(const struct gfs2_sbd *sdp,
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 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
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 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
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 wait_on_holder(struct gfs2_holder *gh)

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 @@ static void gfs2_glmutex_unlock(struct gfs2_glock *gl)
* 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 @@ static void state_change(struct gfs2_glock *gl, unsigned int new_state)
}

gl->gl_state = new_state;
+ gl->gl_tchange = jiffies;
}

/**
@@ -813,7 +840,6 @@ out:
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 @@ static void drop_bh(struct gfs2_glock *gl, unsigned int ret)
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 @@ static void drop_bh(struct gfs2_glock *gl, unsigned int ret)
}

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 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
{
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 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
}

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 @@ static void blocking_cb(struct gfs2_sbd *sdp, struct lm_lockname *name,
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 @@ void gfs2_glock_cb(void *cb_data, unsigned int type, void *data)
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 @@ void gfs2_reclaim_glock(struct gfs2_sbd *sdp)
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 @@ static void clear_glock(struct gfs2_glock *gl)
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 @@ int __init gfs2_glock_init(void)
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
index 88342e0..7ef6b23 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -454,6 +454,7 @@ const struct gfs2_glock_operations gfs2_inode_glops = {
.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 @@ const struct gfs2_glock_operations gfs2_rgrp_glops = {
.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
index 1390b30..23b611a 100644
--- 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 @@ struct gfs2_glock_operations {
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 @@ enum {
GLF_LOCK = 1,
GLF_STICKY = 2,
GLF_DEMOTE = 3,
+ GLF_PENDING_DEMOTE = 4,
GLF_DIRTY = 5,
};

@@ -193,6 +196,7 @@ struct gfs2_glock {

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_glock {
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 {
--
1.5.1.2