Re: [PATCH v2] mm: fix the memory leak after collapsing the huge page fails

[zhong jiang <zhongjiang@huawei.com>]

On 2017/5/10 14:51, Vlastimil Babka wrote:
> On 05/09/2017 03:54 PM, zhong jiang wrote:
>> Hi, Vlastimil
>>
>> I review the code again. it works well for NUMA. because
>> khugepaged_prealloc_page will put_page when *hpage is true.
>>
>> the memory leak will still exist in !NUMA. because it ingore
>> the put_page. is it right? I miss something.
> No, on !NUMA the preallocated and unused new_page is freed by put_page()
> at the very end of khugepaged_do_scan().
 Thank you for clarification. I should consider more before sending the patch.
 
 Thanks
 zhongjiang
>> Thanks
>> zhongjiang
>>
>> On 2017/5/9 20:41, Vlastimil Babka wrote:
>>> On 05/09/2017 02:20 PM, zhong jiang wrote:
>>>> On 2017/5/9 19:34, Vlastimil Babka wrote:
>>>>> On 05/09/2017 12:55 PM, zhongjiang wrote:
>>>>>> From: zhong jiang <zhongjiang@huawei.com>
>>>>>>
>>>>>> Current, when we prepare a huge page to collapse, due to some
>>>>>> reasons, it can fail to collapse. At the moment, we should
>>>>>> release the preallocate huge page.
>>>>>>
>>>>>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>>>>> Hmm, scratch that, there's no memory leak. The pointer to new_page is
>>>>> stored in *hpage, and put_page() is called all the way up in
>>>>> khugepaged_do_scan().
>>>>  I see. I miss it. but why the new_page need to be release all the way.
>>> AFAIK to support preallocation and reusal of preallocated page for
>>> collapse attempt in different pmd. It only works for !NUMA so it's
>>> likely not worth all the trouble and complicated code, so I wouldn't be
>>> opposed to simplifying this.
>>>
>>>>  I do not see the count increment when scan success. it save the memory,
>>>>  only when page fault happen.
>>> I don't understand what you mean here?
>>>
>>>>  Thanks
>>>>  zhongjiang
>>>>>> ---
>>>>>>  mm/khugepaged.c | 4 ++++
>>>>>>  1 file changed, 4 insertions(+)
>>>>>>
>>>>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>>>>> index 7cb9c88..586b1f1 100644
>>>>>> --- a/mm/khugepaged.c
>>>>>> +++ b/mm/khugepaged.c
>>>>>> @@ -1082,6 +1082,8 @@ static void collapse_huge_page(struct mm_struct *mm,
>>>>>>  	up_write(&mm->mmap_sem);
>>>>>>  out_nolock:
>>>>>>  	trace_mm_collapse_huge_page(mm, isolated, result);
>>>>>> +	if (page != NULL && result != SCAN_SUCCEED)
>>>>>> +		put_page(new_page);
>>>>>>  	return;
>>>>>>  out:
>>>>>>  	mem_cgroup_cancel_charge(new_page, memcg, true);
>>>>>> @@ -1555,6 +1557,8 @@ static void collapse_shmem(struct mm_struct *mm,
>>>>>>  	}
>>>>>>  out:
>>>>>>  	VM_BUG_ON(!list_empty(&pagelist));
>>>>>> +	if (page != NULL && result != SCAN_SUCCEED)
>>>>>> +		put_page(new_page);
>>>>>>  	/* TODO: tracepoints */
>>>>>>  }
>>>>>>  
>>>>>>
>>>>> .
>>>>>
>>> .
>>>
>>
>
> .
>


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