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SubjectRe: [PACTH v1] mm, proc: Implement /proc/<pid>/totmaps
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On 2016-08-09 06:30 PM, Jann Horn wrote:
> On Tue, Aug 09, 2016 at 05:01:44PM -0400, Robert Foss wrote:
>> On 2016-08-09 03:24 PM, Jann Horn wrote:
>>> On Tue, Aug 09, 2016 at 12:05:43PM -0400, robert.foss@collabora.com wrote:
>>>> + down_read(&mm->mmap_sem);
>>>> + hold_task_mempolicy(priv);
>>>> +
>>>> + for (vma = mm->mmap; vma != priv->tail_vma; vma = vma->vm_next) {
>>>> + struct mem_size_stats mss;
>>>> + struct mm_walk smaps_walk = {
>>>> + .pmd_entry = smaps_pte_range,
>>>> + .mm = vma->vm_mm,
>>>> + .private = &mss,
>>>> + };
>>>> +
>>>> + if (vma->vm_mm && !is_vm_hugetlb_page(vma)) {
>>>> + memset(&mss, 0, sizeof(mss));
>>>> + walk_page_vma(vma, &smaps_walk);
>>>> + add_smaps_sum(&mss, mss_sum);
>>>> + }
>>>> + }
>>>
>>> Errrr... what? You accumulate values from mem_size_stats items into a
>>> struct mss_sum that is associated with the struct file? So when you
>>> read the file the second time, you get the old values plus the new ones?
>>> And when you read the file in parallel, you get inconsistent values?
>>>
>>> For most files in procfs, the behavior is that you can just call
>>> pread(fd, buf, sizeof(buf), 0) on the same fd again and again, giving
>>> you the current values every time, without mutating state. I strongly
>>> recommend that you get rid of priv->mss and just accumulate the state
>>> in a local variable (maybe one on the stack).
>>
>> So a simple "static struct mem_size_stats" in totmaps_proc_show() would be a
>> better solution?
>
> Er, why "static"? Are you trying to create shared state between different
> readers for some reason?
>

I think I'm a bit confused now, how are you suggesting that I replace
priv->mss?

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