From: Vlastimil Babka <vbabka@suse.cz>
To: Baolin Wang <baolin.wang@linux.alibaba.com>,
David Hildenbrand <david@redhat.com>,
akpm@linux-foundation.org
Cc: mgorman@techsingularity.net, mhocko@suse.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_alloc: consider pfn holes after pfn_valid() in __pageblock_pfn_to_page()
Date: Fri, 14 Apr 2023 17:07:54 +0200 [thread overview]
Message-ID: <e9ac9692-c126-f78f-a6a2-a88eb986ccb7@suse.cz> (raw)
In-Reply-To: <ac8bb4e9-e7f5-f9da-bca0-ac7ef6d68c23@linux.alibaba.com>
On 4/12/23 14:16, Baolin Wang wrote:
>
>
> On 4/12/2023 7:25 PM, David Hildenbrand wrote:
>> On 12.04.23 12:45, Baolin Wang wrote:
>>> Now the __pageblock_pfn_to_page() is used by set_zone_contiguous(),
>>> which checks whether the given zone contains holes, and uses pfn_valid()
>>> to check if the end pfn is valid. However pfn_valid() can not make sure
>>> the end pfn is not a hole if the size of a pageblock is larger than the
>>> size of a sub-mem_section, since the struct page getting by pfn_to_page()
>>> may represent a hole or an unusable page frame, which may cause incorrect
>>> zone contiguous is set.
>>>
>>> Though another user of pageblock_pfn_to_page() in compaction seems work
>>> well now, it is better to avoid scanning or touching these offline pfns.
>>> So like commit 2d070eab2e82 ("mm: consider zone which is not fully
>>> populated to have holes"), we should also use pfn_to_online_page() for
>>> the end pfn to make sure it is a valid pfn with usable page frame.
>>> Meanwhile the pfn_valid() for end pfn can be dropped now.
>>>
>>> Moreover we've already used pfn_to_online_page() for start pfn to make
>>> sure it is online and valid, so the pfn_valid() for the start pfn is
>>> unnecessary, drop it.
>>
>> pageblocks are supposed to fall into a single memory section, so in mos > cases, if the start is online, so is the end.
>
> Yes, the granularity of memory hotplug is a mem_section.
>
> However, suppose the pageblock order is MAX_ORDER-1, and the size of a
> sub-section is 2M, that means a pageblock will fall into 2 sub
> mem-section, and if there is a hole in the zone, that means the 2nd sub
> mem-section can be invalid without setting subsection_map bitmap.
Can that really happen? I think the buddy merging in __free_one_page() would
trip on that?
next prev parent reply other threads:[~2023-04-14 15:07 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-12 10:45 [PATCH] mm/page_alloc: consider pfn holes after pfn_valid() in __pageblock_pfn_to_page() Baolin Wang
2023-04-12 11:15 ` Michal Hocko
2023-04-12 12:24 ` Baolin Wang
2023-04-12 11:25 ` David Hildenbrand
2023-04-12 12:16 ` Baolin Wang
2023-04-14 15:07 ` Vlastimil Babka [this message]
2023-04-19 6:47 ` Baolin Wang
2023-04-20 7:22 ` Huang, Ying
2023-04-20 9:11 ` Baolin Wang
2023-04-21 4:21 ` Huang, Ying
2023-04-21 7:13 ` Baolin Wang
2023-04-21 7:44 ` Huang, Ying
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