linux-kernel - Re: [PATCH v2 5/5] mm/hugetlb: avoid calculating fault_mutex_hash in truncate

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Message-ID: <4b3e9ea6-69e3-493c-342e-92117f274e06@huawei.com>
Date:   Tue, 16 Mar 2021 14:49:31 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, <akpm@...ux-foundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v2 5/5] mm/hugetlb: avoid calculating fault_mutex_hash in
 truncate_op case

On 2021/3/16 11:07, Mike Kravetz wrote:
> On 3/15/21 7:27 PM, Miaohe Lin wrote:
>> The fault_mutex hashing overhead can be avoided in truncate_op case
>> because page faults can not race with truncation in this routine.  So
>> calculate hash for fault_mutex only in !truncate_op case to save some cpu
>> cycles.
>>
>> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> Cc: Mike Kravetz <mike.kravetz@...cle.com>
>> ---
>> v1->v2:
>> remove unnecessary initialization for variable hash
>> collect Reviewed-by tag from Mike Kravetz
> 
> My apologies for not replying sooner and any misunderstanding from my
> previous comments.
> 

That's all right.

> If the compiler is going to produce a warning because the variable is
> not initialized, then we will need to keep the initialization.
> Otherwise, this will show up as a build regression.  Ideally, there
> would be a modifier which could be used to tell the compiler the
> variable will used.  I do not know if such a modifier exists.
> 

I do not know if such a modifier exists too. But maybe not all compilers are intelligent
enough to not produce a warning. It would be safe to keep the initialization...

> The patch can not produce a new warning.  So, if you need to initialize

So just drop this version of the patch? Or should I send a new version with your Reviewed-by tag and
keep the initialization?

> the variable then do it.  My Reviewed-by still applies.
>