Received-SPF: pass (google.com: domain of linux-kernel+bounces-203560-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Message-ID: <7087d0af-93d8-4d49-94f4-dc846a4e2b98@linux.alibaba.com>
Date: Thu, 6 Jun 2024 11:06:23 +0800
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] mm/page_alloc: skip THP-sized PCP list when allocating
 non-CMA THP-sized page
To: yangge1116 <yangge1116@126.com>, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, liuzixing@hygon.cn,
 Johannes Weiner <hannes@cmpxchg.org>, Vlastimil Babka <vbabka@suse.cz>,
 Zi Yan <ziy@nvidia.com>
References: <1717492460-19457-1-git-send-email-yangge1116@126.com>
 <c180d2a0-1e34-41f0-bae8-1205d04a5f6b@linux.alibaba.com>
 <82d31425-86d7-16fa-d09b-fcb203de0986@126.com>
From: Baolin Wang <baolin.wang@linux.alibaba.com>
In-Reply-To: <82d31425-86d7-16fa-d09b-fcb203de0986@126.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit


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.

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));