linux-kernel - Re: [PATCH] mm/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share

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Message-ID: <2fa7aa11-6521-40f3-9934-aba275154ca2@oracle.com>
Date: Thu, 11 Sep 2025 12:54:36 -0700
From: jane.chu@...cle.com
To: David Hildenbrand <david@...hat.com>, harry.yoo@...cle.com,
        osalvador@...e.de, liushixin2@...wei.com, muchun.song@...ux.dev,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: fix copy_hugetlb_page_range() to use
 ->pt_share_count


On 9/9/2025 11:45 PM, David Hildenbrand wrote:
[..]
>> -        /*
>> -         * If the pagetables are shared don't copy or take references.
>> -         *
>> -         * dst_pte == src_pte is the common case of src/dest sharing.
>> -         * However, src could have 'unshared' and dst shares with
>> -         * another vma. So page_count of ptep page is checked instead
>> -         * to reliably determine whether pte is shared.
>> -         */
>> -        if (page_count(virt_to_page(dst_pte)) > 1) {
>> +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
>> +        /* If the pagetables are shared don't copy or take 
>> references. */
> 
> Why remove so much of the original comment?

Because, this part of checking has already advanced from the "dst_pte == 
src_pte" to "page_count() > 1" to ->pt_share_count > 0, it seems cleaner 
to just keep an one liner comment.
That said, if you feel the comments should be kept, I'd be happy to 
restore them with a bit revision.

> 
>> +        if (ptdesc_pmd_pts_count(virt_to_ptdesc(dst_pte)) > 0) {
>>               addr |= last_addr_mask;
>>               continue;
>>           }
> 
> LGTM, thanks!

Thanks!
-jane

>