linux-kernel - Re: [PATCH v1 02/39] mm/rmap: introduce and use hugetlb_remove

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Message-ID: <c6cbf488-89d6-48fc-bd0f-7d666a95e035@redhat.com>
Date:   Mon, 11 Dec 2023 17:35:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1 02/39] mm/rmap: introduce and use hugetlb_remove_rmap()

On 11.12.23 17:33, Matthew Wilcox wrote:
> On Mon, Dec 11, 2023 at 04:56:15PM +0100, David Hildenbrand wrote:
>> hugetlb rmap handling differs quite a lot from "ordinary" rmap code.
>> For example, hugetlb currently only supports entire mappings, and treats
>> any mapping as mapped using a single "logical PTE". Let's move it out
>> of the way so we can overhaul our "ordinary" rmap.
>> implementation/interface.
>>
>> Let's introduce and use hugetlb_remove_rmap() and remove the hugetlb
>> code from page_remove_rmap(). This effectively removes one check on the
>> small-folio path as well.
>>
>> Note: all possible candidates that need care are page_remove_rmap() that
>>        pass compound=true.
>>
>> Reviewed-by: Yin Fengwei <fengwei.yin@...el.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> 
>> +++ b/mm/rmap.c
>> @@ -1482,13 +1482,6 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
>>   
>>   	VM_BUG_ON_PAGE(compound && !PageHead(page), page);
>>   
>> -	/* Hugetlb pages are not counted in NR_*MAPPED */
>> -	if (unlikely(folio_test_hugetlb(folio))) {
>> -		/* hugetlb pages are always mapped with pmds */
>> -		atomic_dec(&folio->_entire_mapcount);
>> -		return;
>> -	}
> 
> Maybe add
> 	VM_BUG_ON_FOLIO(folio_test_hugetlb(folio), folio);
> 

A bulk-add that in patch #6.

Thanks!

-- 
Cheers,

David / dhildenb