linux-kernel - Re: [RFC PATCH v3 0/4] Support large folios for tmpfs

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Message-ID: <584662fb-cb1f-4b2c-9075-f70d31473c9d@linux.alibaba.com>
Date: Wed, 16 Oct 2024 17:29:19 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Kefeng Wang <wangkefeng.wang@...wei.com>, akpm@...ux-foundation.org,
 hughd@...gle.com
Cc: willy@...radead.org, david@...hat.com, 21cnbao@...il.com,
 ryan.roberts@....com, ioworker0@...il.com, da.gomez@...sung.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 0/4] Support large folios for tmpfs



On 2024/10/16 15:49, Kefeng Wang wrote:
> 
> 
> On 2024/10/10 17:58, Baolin Wang wrote:
>> Hi,
>>
>> This RFC patch series attempts to support large folios for tmpfs.
>>
>> Considering that tmpfs already has the 'huge=' option to control the THP
>> allocation, it is necessary to maintain compatibility with the 'huge='
>> option, as well as considering the 'deny' and 'force' option controlled
>> by '/sys/kernel/mm/transparent_hugepage/shmem_enabled'.
>>
>> Add a new huge option 'write_size' to support large folio allocation 
>> based
>> on the write size for tmpfs write and fallocate paths. So the huge pages
>> allocation strategy for tmpfs is that, if the 'huge=' option
>> (huge=always/within_size/advise) is enabled or the 'shmem_enabled' option
>> is 'force', it need just allow PMD sized THP to keep backward 
>> compatibility
>> for tmpfs. While 'huge=' option is disabled (huge=never) or the 
>> 'shmem_enabled'
>> option is 'deny', it will still disable any large folio allocations. Only
>> when the 'huge=' option is 'write_size', it will allow allocating large
>> folios based on the write size.
>>
>> And I think the 'huge=write_size' option should be the default behavior
>> for tmpfs in future.
> 
> Could we avoid new huge= option for tmpfs, maybe support other orders
> for both read/write/fallocate if mount with huge?

Um, I am afraid not, as that would break the 'huge=' compatibility. That 
is to say, users still want PMD-sized huge pages if 'huge=always'.