Re: [PATCH] mm/page_alloc: skip THP-sized PCP list when allocating non-CMA THP-sized page

[yangge1116 <yangge1116@126.com>]

在 2024/6/6 上午11:06, Baolin Wang 写道:
> 
> 
> On 2024/6/4 20:36, yangge1116 wrote:
>>
>>
>> 在 2024/6/4 下午8:01, Baolin Wang 写道:
>>> Cc Johannes, Zi and Vlastimil.
>>>
>>> On 2024/6/4 17:14, yangge1116@126.com wrote:
>>>> From: yangge <yangge1116@126.com>
>>>>
>>>> Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for
>>>> THP-sized allocations") no longer differentiates the migration type
>>>> of pages in THP-sized PCP list, it's possible to get a CMA page from
>>>> the list, in some cases, it's not acceptable, for example, allocating
>>>> a non-CMA page with PF_MEMALLOC_PIN flag returns a CMA page.
>>>>
>>>> The patch forbids allocating non-CMA THP-sized page from THP-sized
>>>> PCP list to avoid the issue above.
>>>>
>>>> Fixes: 5d0a661d808f ("mm/page_alloc: use only one PCP list for 
>>>> THP-sized allocations")
>>>> Signed-off-by: yangge <yangge1116@126.com>
>>>> ---
>>>>   mm/page_alloc.c | 10 ++++++++++
>>>>   1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>> index 2e22ce5..0bdf471 100644
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -2987,10 +2987,20 @@ struct page *rmqueue(struct zone 
>>>> *preferred_zone,
>>>>       WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
>>>>       if (likely(pcp_allowed_order(order))) {
>>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>> +        if (!IS_ENABLED(CONFIG_CMA) || alloc_flags & ALLOC_CMA ||
>>>> +                        order != HPAGE_PMD_ORDER) {
>>>
>>> Seems you will also miss the non-CMA THP from the PCP, so I wonder if 
>>> we can add a migratetype comparison in __rmqueue_pcplist(), and if 
>>> it's not suitable, then fallback to buddy?
>>
>> Yes, we may miss some non-CMA THPs in the PCP. But, if add a 
>> migratetype comparison in __rmqueue_pcplist(), we may need to compare 
>> many times because of pcp batch.
> 
> I mean we can only compare once, focusing on CMA pages.

pcp_list may contains CMA and no-CMA pages, why only compare once, just 
increase one chance of using the pcp_list?


> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3734fe7e67c0..960a3b5744d8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2973,6 +2973,11 @@ struct page *__rmqueue_pcplist(struct zone *zone, 
> unsigned int order,
>                  }
> 
>                  page = list_first_entry(list, struct page, pcp_list);
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +               if (order == HPAGE_PMD_ORDER && 
> !is_migrate_movable(migratetype) &&
> +                   is_migrate_cma(get_pageblock_migratetype(page)))
> +                       return NULL;
> +#endif
>                  list_del(&page->pcp_list);
>                  pcp->count -= 1 << order;
>          } while (check_new_pages(page, order));