Re: [PATCH 2.6.21-rc3-mm2 3/4] futex_requeue_pi optimization

Pierre Peiffer
2007-03-20T15:33:23Z

Peter Zijlstra a écrit :
>> +static void *get_futex_address(union futex_key *key)
>> +{
>> + void *uaddr;
>> +
>> + if (key->both.offset & 1) {
>> + /* shared mapping */
>> + uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT)
>> + + key->shared.offset - 1);
>> + } else {
>> + /* private mapping */
>> + uaddr = (void*)(key->private.address + key->private.offset);
>> + }
>> +
>> + return uaddr;
>> +}
>
> This will not work for nonlinear vmas, granted, not a lot of ppl stick
> futexes in nonlinear vmas, but the futex_key stuff handles it, this
> doesn't.

Indeed ! Thanks for pointing me to this.

Since I'm not familiar with vmm, does this code look more correct to you ?

static void *get_futex_address(union futex_key *key)
{
void *uaddr;
struct vm_area_struct *vma = current->mm->mmap;

if (key->both.offset & 1) {
/* shared mapping */
struct file * vmf;

do {
if ((vmf = vma->vm_file)
&& (key->shared.inode == vmf->f_dentry->d_inode))
break;
vma = vma->vm_next;
} while (vma);

if (likely(!(vma->vm_flags & VM_NONLINEAR)))
uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT)
+ key->shared.offset - 1);
else
uaddr = (void*) vma->vm_start
+ ((key->shared.pgoff - vma->vm_pgoff)
<< PAGE_SHIFT)
+ key->shared.offset - 1;
} else {
/* private mapping */
uaddr = (void*)(key->private.address + key->private.offset);
}

return uaddr;
}

Or is there a more direct way to retrieve the vma corresponding to the given inode ?

Thanks,

--
Pierre