linux-kernel - Re: [PATCH 3/4] mm/hugeltb: fix potential wrong gbl_reserve value for hugetlb_acct

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Message-ID: <b3658faa-ed18-2421-9960-df732f7a59cc@huawei.com>
Date:   Fri, 9 Apr 2021 14:36:04 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, <akpm@...ux-foundation.org>
CC:     <n-horiguchi@...jp.nec.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [PATCH 3/4] mm/hugeltb: fix potential wrong gbl_reserve value for
 hugetlb_acct_memory()

On 2021/4/9 12:37, Mike Kravetz wrote:
> On 4/8/21 8:01 PM, Miaohe Lin wrote:
>> On 2021/4/9 6:53, Mike Kravetz wrote:
>>>
>>> Yes, add a comment to hugetlb_unreserve_pages saying that !resv_map
>>> implies freed == 0.
>>>
>>
>> Sounds good!
>>
>>> It would also be helpful to check for (chg - freed) == 0 and skip the
>>> calls to hugepage_subpool_put_pages() and hugetlb_acct_memory().  Both
>>> of those routines may perform an unnecessary lock/unlock cycle in this
>>> case.
>>>
>>> A simple
>>> 	if (chg == free)
>>> 		return 0;
>>> before the call to hugepage_subpool_put_pages would work.
>>
>> This may not be really helpful because hugepage_subpool_put_pages() and hugetlb_acct_memory()
>> both would handle delta == 0 case without unnecessary lock/unlock cycle.
>> Does this make sense for you? If so, I will prepare v2 with the changes to add a comment
>> to hugetlb_unreserve_pages() __without__ the check for (chg - freed) == 0.
> 
> Sorry, I forgot about the recent changes to check for delta == 0.
> No need for the check here, just the comment.
> 

That's all right. Will add the comment in V2.
Thanks.