On 4/4/24 2:19 PM, Baolin Wang wrote:
>
>
> On 2024/4/4 18:03, Vlastimil Babka wrote:
>> On 4/3/24 3:47 PM, Baolin Wang wrote:
>>> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
>>> on the per-cpu lists") extends the PCP allocator to store THP pages, and
>>> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
>>> But the pageblock_order is not always equal to THP order, it might also
>>> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>>>
>>> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
>>> THP for PCP can fix this issue
>>>
>>> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
>>> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>
>> IIUC this happens with CONFIG_HUGETLB_PAGE disabled because HUGETLBFS is
>> disabled? But THPs are still enabled? I think there might be more of THP
>
> Right, and seems the Powerpc arch will set pageblock_order via
> set_pageblock_order() when the huge page sizes are variable (not sure if
> this is always equal to THP order).
>
> Moreover, it still does not make sense to use pageblock_order to
> indicate a THP page, especially when we already have HPAGE_PMD_ORDER to
> represent THP.
>
>> working suboptimally in that case with pageblock_order being larger
>> (MAX_PAGE_ORDER).
>>
>> In other words, should be rather make pageblock_order itself defined as
>>
>> min_t(unsigned int, HPAGE_PMD_ORDER, MAX_PAGE_ORDER)
>>
>> in case with !CONFIG_HUGETLB_PAGE but THP enabled.
>
> Yes, this makes sense to me (I wonder why this wasn't done before?). I
> can create a seperate patch to do this, what do you think? Thanks.
It probably wasn't anticipated that hugetlbfs would be disabled and THP
enabled. If you can create such patch, great!
