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Commit 5b52fc89 authored by Stephen Wilson's avatar Stephen Wilson Committed by Linus Torvalds
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proc: allocate storage for numa_maps statistics once 



In show_numa_map() we collect statistics into a numa_maps structure.
Since the number of NUMA nodes can be very large, this structure is not a
candidate for stack allocation.

Instead of going thru a kmalloc()+kfree() cycle each time show_numa_map()
is invoked, perform the allocation just once when /proc/pid/numa_maps is
opened.

Performing the allocation when numa_maps is opened, and thus before a
reference to the target tasks mm is taken, eliminates a potential
stalemate condition in the oom-killer as originally described by Hugh
Dickins:

  ... imagine what happens if the system is out of memory, and the mm
  we're looking at is selected for killing by the OOM killer: while
  we wait in __get_free_page for more memory, no memory is freed
  from the selected mm because it cannot reach exit_mmap while we hold
  that reference.

Signed-off-by: default avatarStephen Wilson <wilsons@start.ca>
Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f2beb798

fs/proc/task_mmu.c

+27 −9
Original line number Diff line number Diff line
@@ -871,6 +871,11 @@ struct numa_maps { 
	unsigned long node[MAX_NUMNODES];

};



struct numa_maps_private {

	struct proc_maps_private proc_maps;

	struct numa_maps md;

};



static void gather_stats(struct page *page, struct numa_maps *md, int pte_dirty)

{

	int count = page_mapcount(page);
@@ -963,9 +968,10 @@ static int gather_hugetbl_stats(pte_t *pte, unsigned long hmask, 
 */

static int show_numa_map(struct seq_file *m, void *v)

{

	struct proc_maps_private *priv = m->private;

	struct numa_maps_private *numa_priv = m->private;

	struct proc_maps_private *proc_priv = &numa_priv->proc_maps;

	struct vm_area_struct *vma = v;

	struct numa_maps *md;

	struct numa_maps *md = &numa_priv->md;

	struct file *file = vma->vm_file;

	struct mm_struct *mm = vma->vm_mm;

	struct mm_walk walk = {};
@@ -976,9 +982,8 @@ static int show_numa_map(struct seq_file *m, void *v) 
	if (!mm)

		return 0;



	md = kzalloc(sizeof(struct numa_maps), GFP_KERNEL);

	if (!md)

		return 0;

	/* Ensure we start with an empty set of numa_maps statistics. */

	memset(md, 0, sizeof(*md));



	md->vma = vma;
@@ -987,7 +992,7 @@ static int show_numa_map(struct seq_file *m, void *v) 
	walk.private = md;

	walk.mm = mm;



	pol = get_vma_policy(priv->task, vma, vma->vm_start);

	pol = get_vma_policy(proc_priv->task, vma, vma->vm_start);

	mpol_to_str(buffer, sizeof(buffer), pol, 0);

	mpol_cond_put(pol);
@@ -1034,12 +1039,12 @@ static int show_numa_map(struct seq_file *m, void *v) 
			seq_printf(m, " N%d=%lu", n, md->node[n]);

out:

	seq_putc(m, '\n');

	kfree(md);



	if (m->count < m->size)

		m->version = (vma != priv->tail_vma) ? vma->vm_start : 0;

		m->version = (vma != proc_priv->tail_vma) ? vma->vm_start : 0;

	return 0;

}



static const struct seq_operations proc_pid_numa_maps_op = {

        .start  = m_start,

        .next   = m_next,
@@ -1049,7 +1054,20 @@ static const struct seq_operations proc_pid_numa_maps_op = { 


static int numa_maps_open(struct inode *inode, struct file *file)

{

	return do_maps_open(inode, file, &proc_pid_numa_maps_op);

	struct numa_maps_private *priv;

	int ret = -ENOMEM;

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);

	if (priv) {

		priv->proc_maps.pid = proc_pid(inode);

		ret = seq_open(file, &proc_pid_numa_maps_op);

		if (!ret) {

			struct seq_file *m = file->private_data;

			m->private = priv;

		} else {

			kfree(priv);

		}

	}

	return ret;

}



const struct file_operations proc_numa_maps_operations = {