linux-kernel - Re: [PATCH 1/8] mm: move highest_order() and next

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Date: Wed, 8 May 2024 17:40:19 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Ryan Roberts <ryan.roberts@....com>, akpm@...ux-foundation.org,
 hughd@...gle.com
Cc: willy@...radead.org, david@...hat.com, ioworker0@...il.com,
 wangkefeng.wang@...wei.com, ying.huang@...el.com, 21cnbao@...il.com,
 shy828301@...il.com, ziy@...dia.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] mm: move highest_order() and next_order() out of the
 THP config



On 2024/5/8 17:06, Ryan Roberts wrote:
> On 08/05/2024 03:13, Baolin Wang wrote:
>>
>>
>> On 2024/5/7 18:21, Ryan Roberts wrote:
>>> On 06/05/2024 09:46, Baolin Wang wrote:
>>>> Move highest_order() and next_order() out of the CONFIG_TRANSPARENT_HUGEPAGE
>>>> macro, which can be common functions to be used.
>>>
>>> Sorry if I haven't kept up with the discussion, but why is this needed? I
>>> wouldn't expect a need to iterate over orders if THP is compile-time disabled
>>> because we will never try to allocate THP?
>>
>> Cause I don't want to add some dummy functions to avoid building errors if
>> CONFIG_TRANSPARENT_HUGEPAGE is not enabled in patch 6. Another thought is that
>> the pagecache can also allocate a large folio even when THP is not enabled, so
>> these helpers may be used in the future (not sure though).
> 
> OK, I'll admit I haven't looked at the latter patches yet - I'd like to conclude
> on the interface and mapping/alignment strategy first.
> 
> But it wasn't necessary to access these functions for the anon/private case
> without CONFIG_TRANSPARENT_HUGEPAGE, so I'm wondering why it's needed for shmem
> case. I would expect that they don't need to be defined at all.

Currently in the shmem_alloc_and_add_folio() function, the hugepage 
allocating is not guarded with '#ifdef CONFIG_TRANSPARENT_HUGEPAGE', but 
rather with 'IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)', which can lead to 
some building errors when CONFIG_TRANSPARENT_HUGEPAGE is not enabled. 
However, this is not a big issue, and I will make some adjustments to 
avoid defining dummy functions.