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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

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.