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From: Miaohe Lin <linmiaohe@huawei.com>
To: Muchun Song <muchun.song@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	<mike.kravetz@oracle.com>, Muchun Song <songmuchun@bytedance.com>,
	<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 03/10] hugetlb: Use LIST_HEAD() to define a list head
Date: Sat, 27 Aug 2022 14:38:54 +0800	[thread overview]
Message-ID: <2339d458-8b98-f540-22f1-50b772eef130@huawei.com> (raw)
In-Reply-To: <83DBE074-0B63-4CB2-9BD2-65967977B69C@linux.dev>

On 2022/8/27 10:48, Muchun Song wrote:
> 
> 
>> On Aug 27, 2022, at 10:27, Miaohe Lin <linmiaohe@huawei.com> wrote:
>>
>> On 2022/8/27 9:47, Muchun Song wrote:
>>>
>>>
>>>> On Aug 26, 2022, at 17:24, Miaohe Lin <linmiaohe@huawei.com> wrote:
>>>>
>>>> We can avoid unneeded WRITE_ONCE() overhead by using LIST_HEAD() to define
>>>> a list head.
>>>
>>> IIUC, the overhead doesn’t change. Right?
>>
>> I think the overhead is changed. LIST_HEAD is initialized without using WRITE_ONCE():
> 
> I think there is no special difference with "WRITE_ONCE(var, 0)" vs "var = 0” in

It's not write var to 0 indeed. But there seems are no special difference.

> assembly code. Both code of line will be compiled to a mov or movq instruction.
> I didn’t confirm if the assembly code is different (I tend to think it is similar).
> Just some analysis from me.

I checked the generated code in x86, they're almost same. And in aarch64, there's difference
between one "stp" instruction vs two "str" instruction. So I think you're right. Thanks for
pointing this out. I should tweak the commit log in next version.

Thanks a lot,
Miaohe Lin


  reply	other threads:[~2022-08-27  6:39 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-26  9:24 [PATCH 00/10] A few cleanup patches for hugetlb Miaohe Lin
2022-08-26  9:24 ` [PATCH 01/10] hugetlb: make hugetlb_cma_check() static Miaohe Lin
2022-08-27  1:40   ` Muchun Song
2022-08-26  9:24 ` [PATCH 02/10] hugetlb: Use helper macro SZ_1K Miaohe Lin
2022-08-27  1:40   ` Muchun Song
2022-08-26  9:24 ` [PATCH 03/10] hugetlb: Use LIST_HEAD() to define a list head Miaohe Lin
2022-08-27  1:47   ` Muchun Song
2022-08-27  2:27     ` Miaohe Lin
2022-08-27  2:48       ` Muchun Song
2022-08-27  6:38         ` Miaohe Lin [this message]
2022-08-26  9:24 ` [PATCH 04/10] hugetlb: Use sizeof() to get the array size Miaohe Lin
2022-08-27  1:43   ` Muchun Song
2022-08-26  9:24 ` [PATCH 05/10] hugetlb: Use helper {huge_pte|pmd}_lock() Miaohe Lin
2022-08-27  1:48   ` Muchun Song
2022-08-26  9:24 ` [PATCH 06/10] hugetlb: pass NULL to kobj_to_hstate() if nid is unused Miaohe Lin
2022-08-27  1:49   ` Muchun Song
2022-08-26  9:24 ` [PATCH 07/10] hugetlb: kill hugetlbfs_pagecache_page() Miaohe Lin
2022-08-27  1:52   ` Muchun Song
2022-08-26  9:24 ` [PATCH 08/10] hugetlb: remove unneeded SetHPageVmemmapOptimized() Miaohe Lin
2022-08-27  1:35   ` Muchun Song
2022-08-27  2:18     ` Miaohe Lin
2022-08-27  2:56       ` Muchun Song
2022-08-26  9:24 ` [PATCH 09/10] hugetlb: remove meaningless BUG_ON(huge_pte_none()) Miaohe Lin
2022-08-27  2:03   ` Muchun Song
2022-08-26  9:24 ` [PATCH 10/10] hugetlb: make hugetlb selects SYSFS if !SYSCTL Miaohe Lin
2022-08-27  1:59   ` Muchun Song
2022-08-27  2:34     ` Miaohe Lin

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