[PATCH 1/2] hugepage: Protect region tracking lists with its ownspinlock

From: Anton Blanchard
Date: Mon Jan 24 2011 - 22:32:59 EST



In preparation for creating a hash of spinlocks to replace the global
hugetlb_instantiation_mutex, protect the region tracking code with
its own spinlock.

Signed-off-by: Anton Blanchard <anton@xxxxxxxxx>
---

The old code locked it with either:

down_write(&mm->mmap_sem);
or
down_read(&mm->mmap_sem);
mutex_lock(&hugetlb_instantiation_mutex);

I chose to keep things simple and wrap everything with a single lock.
Do we need the parallelism the old code had in the down_write case?


Index: powerpc.git/mm/hugetlb.c
===================================================================
--- powerpc.git.orig/mm/hugetlb.c 2011-01-07 12:50:52.090440484 +1100
+++ powerpc.git/mm/hugetlb.c 2011-01-07 12:52:03.922704453 +1100
@@ -56,16 +56,6 @@ static DEFINE_SPINLOCK(hugetlb_lock);
/*
* Region tracking -- allows tracking of reservations and instantiated pages
* across the pages in a mapping.
- *
- * The region data structures are protected by a combination of the mmap_sem
- * and the hugetlb_instantion_mutex. To access or modify a region the caller
- * must either hold the mmap_sem for write, or the mmap_sem for read and
- * the hugetlb_instantiation mutex:
- *
- * down_write(&mm->mmap_sem);
- * or
- * down_read(&mm->mmap_sem);
- * mutex_lock(&hugetlb_instantiation_mutex);
*/
struct file_region {
struct list_head link;
@@ -73,10 +63,14 @@ struct file_region {
long to;
};

+static DEFINE_SPINLOCK(region_lock);
+
static long region_add(struct list_head *head, long f, long t)
{
struct file_region *rg, *nrg, *trg;

+ spin_lock(&region_lock);
+
/* Locate the region we are either in or before. */
list_for_each_entry(rg, head, link)
if (f <= rg->to)
@@ -106,6 +100,7 @@ static long region_add(struct list_head
}
nrg->from = f;
nrg->to = t;
+ spin_unlock(&region_lock);
return 0;
}

@@ -114,6 +109,8 @@ static long region_chg(struct list_head
struct file_region *rg, *nrg;
long chg = 0;

+ spin_lock(&region_lock);
+
/* Locate the region we are before or in. */
list_for_each_entry(rg, head, link)
if (f <= rg->to)
@@ -124,14 +121,17 @@ static long region_chg(struct list_head
* size such that we can guarantee to record the reservation. */
if (&rg->link == head || t < rg->from) {
nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
- if (!nrg)
- return -ENOMEM;
+ if (!nrg) {
+ chg = -ENOMEM;
+ goto out;
+ }
nrg->from = f;
nrg->to = f;
INIT_LIST_HEAD(&nrg->link);
list_add(&nrg->link, rg->link.prev);

- return t - f;
+ chg = t - f;
+ goto out;
}

/* Round our left edge to the current segment if it encloses us. */
@@ -144,7 +144,7 @@ static long region_chg(struct list_head
if (&rg->link == head)
break;
if (rg->from > t)
- return chg;
+ goto out;

/* We overlap with this area, if it extends futher than
* us then we must extend ourselves. Account for its
@@ -155,6 +155,9 @@ static long region_chg(struct list_head
}
chg -= rg->to - rg->from;
}
+out:
+
+ spin_unlock(&region_lock);
return chg;
}

@@ -163,12 +166,16 @@ static long region_truncate(struct list_
struct file_region *rg, *trg;
long chg = 0;

+ spin_lock(&region_lock);
+
/* Locate the region we are either in or before. */
list_for_each_entry(rg, head, link)
if (end <= rg->to)
break;
- if (&rg->link == head)
- return 0;
+ if (&rg->link == head) {
+ chg = 0;
+ goto out;
+ }

/* If we are in the middle of a region then adjust it. */
if (end > rg->from) {
@@ -185,6 +192,9 @@ static long region_truncate(struct list_
list_del(&rg->link);
kfree(rg);
}
+
+out:
+ spin_unlock(&region_lock);
return chg;
}

@@ -193,6 +203,8 @@ static long region_count(struct list_hea
struct file_region *rg;
long chg = 0;

+ spin_lock(&region_lock);
+
/* Locate each segment we overlap with, and count that overlap. */
list_for_each_entry(rg, head, link) {
int seg_from;
@@ -209,6 +221,7 @@ static long region_count(struct list_hea
chg += seg_to - seg_from;
}

+ spin_unlock(&region_lock);
return chg;
}

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/