linux-kernel - Re: [PATCH 4/8] hugetlb: create remove_hugetlb

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Message-ID: <def1f500-ae75-5669-5a3d-0472865d2d4c@oracle.com>
Date:   Fri, 26 Mar 2021 12:57:55 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Rientjes <rientjes@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Hillf Danton <hdanton@...a.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/8] hugetlb: create remove_hugetlb_page() to separate
 functionality

On 3/25/21 7:10 PM, Miaohe Lin wrote:
> On 2021/3/25 8:28, Mike Kravetz wrote:
>> The new remove_hugetlb_page() routine is designed to remove a hugetlb
>> page from hugetlbfs processing.  It will remove the page from the active
>> or free list, update global counters and set the compound page
>> destructor to NULL so that PageHuge() will return false for the 'page'.
>> After this call, the 'page' can be treated as a normal compound page or
>> a collection of base size pages.
>>
>> remove_hugetlb_page is to be called with the hugetlb_lock held.
>>
>> Creating this routine and separating functionality is in preparation for
>> restructuring code to reduce lock hold times.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
>> ---
>>  mm/hugetlb.c | 70 +++++++++++++++++++++++++++++++++-------------------
>>  1 file changed, 45 insertions(+), 25 deletions(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 404b0b1c5258..3938ec086b5c 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1327,6 +1327,46 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>>  						unsigned int order) { }
>>  #endif
>>  
>> +/*
>> + * Remove hugetlb page from lists, and update dtor so that page appears
>> + * as just a compound page.  A reference is held on the page.
>> + * NOTE: hugetlb specific page flags stored in page->private are not
>> + *	 automatically cleared.  These flags may be used in routines
>> + *	 which operate on the resulting compound page.
> 
> It seems HPageFreed and HPageTemporary is cleared. Which hugetlb specific page flags
> is reserverd here and why? Could you please give a simple example to clarify
> this in the comment to help understand this NOTE?
> 

I will remove that NOTE: in the comment to avoid any confusion.

The NOTE was add in the RFC that contained a separate patch to add a flag
that tracked huge pages allocated from CMA.  That flag needed to remain
for subsequent freeing of such pages.  This is no longer needed.

> The code looks good to me. Many thanks!
> Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thanks,
-- 
Mike Kravetz