[Devel] Re: [v12][PATCH 1/9] Factor out code to allocate pidmap page

[Sukadev Bhattiprolu]

Cc LKML

Sukadev Bhattiprolu [sukadev at linux.vnet.ibm.com] wrote:
| 
| Subject: [v12][PATCH 1/9] Factor out code to allocate pidmap page
| 
| To simplify alloc_pidmap(), move code to allocate a pid map page to a
| separate function.
| 
| Changelog[v3]:
| 	- Earlier version of patchset called alloc_pidmap_page() from two
| 	  places. But now its called from only one place. Even so, moving
| 	  this code out into a separate function simplifies alloc_pidmap().
| Changelog[v2]:
| 	- (Matt Helsley, Dave Hansen) Have alloc_pidmap_page() return
| 	  -ENOMEM on error instead of -1.
| 
| Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
| Acked-by: Serge Hallyn <serue at us.ibm.com>
| Reviewed-by: Oren Laadan <orenl at cs.columbia.edu>
| ---
|  kernel/pid.c |   45 ++++++++++++++++++++++++++++++---------------
|  1 files changed, 30 insertions(+), 15 deletions(-)
| 
| diff --git a/kernel/pid.c b/kernel/pid.c
| index d3f722d..7d4bb6e 100644
| --- a/kernel/pid.c
| +++ b/kernel/pid.c
| @@ -122,9 +122,35 @@ static void free_pidmap(struct upid *upid)
|  	atomic_inc(&map->nr_free);
|  }
| 
| +static int alloc_pidmap_page(struct pidmap *map)
| +{
| +	void *page;
| +
| +	if (likely(map->page))
| +		return 0;
| +
| +	page = kzalloc(PAGE_SIZE, GFP_KERNEL);
| +
| +	/*
| +	 * Free the page if someone raced with us installing it:
| +	 */
| +	spin_lock_irq(&pidmap_lock);
| +	if (map->page)
| +		kfree(page);
| +	else
| +		map->page = page;
| +	spin_unlock_irq(&pidmap_lock);
| +
| +	if (unlikely(!map->page))
| +		return -ENOMEM;
| +
| +	return 0;
| +}
| +
|  static int alloc_pidmap(struct pid_namespace *pid_ns)
|  {
|  	int i, offset, max_scan, pid, last = pid_ns->last_pid;
| +	int rc;
|  	struct pidmap *map;
| 
|  	pid = last + 1;
| @@ -134,21 +160,10 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
|  	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
|  	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
|  	for (i = 0; i <= max_scan; ++i) {
| -		if (unlikely(!map->page)) {
| -			void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
| -			/*
| -			 * Free the page if someone raced with us
| -			 * installing it:
| -			 */
| -			spin_lock_irq(&pidmap_lock);
| -			if (map->page)
| -				kfree(page);
| -			else
| -				map->page = page;
| -			spin_unlock_irq(&pidmap_lock);
| -			if (unlikely(!map->page))
| -				break;
| -		}
| +		rc = alloc_pidmap_page(map);
| +		if (rc)
| +			break;
| +
|  		if (likely(atomic_read(&map->nr_free))) {
|  			do {
|  				if (!test_and_set_bit(offset, map->page)) {
| -- 
| 1.6.0.4
| 
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