Re: [PATCH 2/4] mm: compaction: convert to folio_isolate_movable()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/8/29 9:11, Baolin Wang wrote:
> 
> 
> On 2024/8/29 07:37, Vishal Moola wrote:
>> On Wed, Aug 28, 2024 at 08:36:03PM +0800, Kefeng Wang wrote:
>>>
>>>
>>> On 2024/8/28 18:04, Baolin Wang wrote:
>>>> Hi Kefeng,
>>>>
>>>> On 2024/8/26 12:01, Kefeng Wang wrote:
>>>>> The tail page will always fail to isolate for non-lru-movable and
>>>>> LRU page in isolate_migratepages_block(), so move PageTail check
>>>>> ahead, then convert to use folio_isolate_movable() helper and more
>>>>> folios.
>>>>>
>>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>>>> ---
>>>>>    mm/compaction.c | 32 +++++++++++++++++---------------
>>>>>    1 file changed, 17 insertions(+), 15 deletions(-)
>>>>>
>>>>> diff --git a/mm/compaction.c b/mm/compaction.c
>>>>> index a2b16b08cbbf..aa2e8bb9fa58 100644
>>>>> --- a/mm/compaction.c
>>>>> +++ b/mm/compaction.c
>>>>> @@ -1074,39 +1074,41 @@ isolate_migratepages_block(struct
>>>>> compact_control *cc, unsigned long low_pfn,
>>>>>                }
>>>>>            }
>>>>> +        if (PageTail(page))
>>>>> +            goto isolate_fail;
>>>>> +
>>>>> +        folio = page_folio(page);
>>>>
>>>> I wonder if this is stable. Before page_folio(), it does not hold a
>>>> reference on the page, so seems we should re-check the folio still
>>>> contains this page after gaining a reference on the folio?
>>>
>>> Oh, you are right, so two way to avoid this,
>>>
>>> 1) re-check 'page_folio(page)  == folio', but this need change a little
>>> more.
>>>
>>> 2)  directly use folio_get_nontail_page(page) here, and folio_put in the
>>> following path, this will try to get for any pages, but it should be
>>> accepted ?
>>>
>>> I'd prefer 2) but any other suggestion?
>>
>> I think option 2 makes sense, and simply use folio_put() on success and
>> goto isolate_fail_put on failure instead of isolate_fail.
>>
>> With option 2, it might make sense to have folio_isolate_movable()
>> expect to be passed a folio with elevated refcount. Then it could be
>> treated similarly to its sister function folio_isolate_lru() and simply
>> use folio_get() for its reference.
> 
> Yes, that makes sense to me too.

Thanks Vishal/Baolin, will refresh and send v2.