Messages in this thread | | | Date | Wed, 17 Oct 2012 21:35:53 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [patch for-3.7 v2] mm, mempolicy: avoid taking mutex inside spinlock when reading numa_maps |
| |
On Thu, 18 Oct 2012, Kamezawa Hiroyuki wrote:
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 14df880..d92e868 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -94,6 +94,11 @@ static void vma_stop(struct proc_maps_private *priv, struct > vm_area_struct *vma) > { > if (vma && vma != priv->tail_vma) { > struct mm_struct *mm = vma->vm_mm; > +#ifdef CONFIG_NUMA > + task_lock(priv->task); > + __mpol_put(priv->task->mempolicy); > + task_unlock(priv->task); > +#endif > up_read(&mm->mmap_sem); > mmput(mm); > } > @@ -130,6 +135,16 @@ static void *m_start(struct seq_file *m, loff_t *pos) > return mm; > down_read(&mm->mmap_sem); > + /* > + * task->mempolicy can be freed even if mmap_sem is down (see > kernel/exit.c) > + * We grab refcount for stable access. > + * repleacement of task->mmpolicy is guarded by mmap_sem. > + */ > +#ifdef CONFIG_NUMA > + task_lock(priv->task); > + mpol_get(priv->task->mempolicy); > + task_unlock(priv->task); > +#endif > tail_vma = get_gate_vma(priv->task->mm); > priv->tail_vma = tail_vma; > @@ -161,6 +176,11 @@ out: > /* End of vmas has been reached */ > m->version = (tail_vma != NULL)? 0: -1UL; > +#ifdef CONFIG_NUMA > + task_lock(priv->task); > + __mpol_put(priv->task->mempolicy); > + task_unlock(priv->task); > +#endif > up_read(&mm->mmap_sem); > mmput(mm); > return tail_vma;
Yes, I must admit that this is better than my version and it looks like all the ->show() functions that use these start, next, stop functions don't take task_lock() and this would generally be useful: we already hold current->mm->mmap_sem so there is little harm in holding task_lock(current) when reading these files as long as we're not touching the fastpath.
These routines seem like it would nicely be added to mempolicy.h since we depend on CONFIG_NUMA there already.
Please fix up the mess I made in show_numa_map() in 32f8516a8c73 ("mm, mempolicy: fix printing stack contents in numa_maps") by simply removing the task_lock() and task_unlock() as part of your patch.
Thanks Kame!
| |