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Message-ID: <e1e6867f-ed97-49f0-8272-8cdc0f6463b0@linux.alibaba.com>
Date: Wed, 8 May 2024 13:45:48 +0800
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Subject: Re: [PATCH 0/8] add mTHP support for anonymous shmem
To: Ryan Roberts <ryan.roberts@arm.com>, akpm@linux-foundation.org,
 hughd@google.com
Cc: willy@infradead.org, david@redhat.com, ioworker0@gmail.com,
 wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com,
 shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
References: <cover.1714978902.git.baolin.wang@linux.alibaba.com>
 <d887b469-312f-433b-b7a1-a290a381d4d5@arm.com>
From: Baolin Wang <baolin.wang@linux.alibaba.com>
In-Reply-To: <d887b469-312f-433b-b7a1-a290a381d4d5@arm.com>
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On 2024/5/7 18:20, Ryan Roberts wrote:
> On 06/05/2024 09:46, Baolin Wang wrote:
>> Anonymous pages have already been supported for multi-size (mTHP) allocation
>> through commit 19eaf44954df, that can allow THP to be configured through the
>> sysfs interface located at '/sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled'.
>>
>> However, the anonymous shared pages will ignore the anonymous mTHP rule
>> configured through the sysfs interface, and can only use the PMD-mapped
>> THP, that is not reasonable. Many implement anonymous page sharing through
>> mmap(MAP_SHARED | MAP_ANONYMOUS), especially in database usage scenarios,
>> therefore, users expect to apply an unified mTHP strategy for anonymous pages,
>> also including the anonymous shared pages, in order to enjoy the benefits of
>> mTHP. For example, lower latency than PMD-mapped THP, smaller memory bloat
>> than PMD-mapped THP, contiguous PTEs on ARM architecture to reduce TLB miss etc.
>>
>> The primary strategy is similar to supporting anonymous mTHP. Introduce
>> a new interface '/mm/transparent_hugepage/hugepage-XXkb/shmem_enabled',
>> which can have all the same values as the top-level
> 
> Didn't we agree that "force" would not be supported for now, and would return an
> error when attempting to set for a non-PMD-size hugepage-XXkb/shmem_enabled (or
> indirectly through inheritance)?

Yes. Sorry, I did not explain it in detail in the cover letter. Please 
see patch 5 you already commented.