linux-kernel - Re: [RFC PATCH v2 12/47] hugetlb: add hugetlb_hgm_walk and hugetlb_walk

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Message-ID: <f9f271b6-9888-7e92-8054-f48a9ca3e233@oracle.com>
Date:   Wed, 4 Jan 2023 17:12:33 -0800
From:   Jane Chu <jane.chu@...cle.com>
To:     James Houghton <jthoughton@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 12/47] hugetlb: add hugetlb_hgm_walk and
 hugetlb_walk_step



On 1/4/2023 4:57 PM, Jane Chu wrote:
>> + * @stop_at_none determines what we do when we encounter an empty 
>> PTE. If true,
>> + * we return that PTE. If false and @sz is less than the current 
>> PTE's size,
>> + * we make that PTE point to the next level down, going until @sz is 
>> the same
>> + * as our current PTE.
> [..]
>> +int hugetlb_hgm_walk(struct mm_struct *mm, struct vm_area_struct *vma,
>> +             struct hugetlb_pte *hpte, unsigned long addr,
>> +             unsigned long sz, bool stop_at_none)
>> +{

Also here below, the way 'stop_at_none' is used when HGM isn't enabled
is puzzling.  Could you elaborate please?

+	if (!hugetlb_hgm_enabled(vma)) {
+		if (stop_at_none)
+			return 0;
+		return sz == huge_page_size(hstate_vma(vma)) ? 0 : -EINVAL;
+	}

> [..]
>> +    while (hugetlb_pte_size(hpte) > sz && !ret) {
>> +        pte = huge_ptep_get(hpte->ptep);
>> +        if (!pte_present(pte)) {
>> +            if (stop_at_none)
>> +                return 0;
>> +            if (unlikely(!huge_pte_none(pte)))
>> +                return -EEXIST;
> 
> If 'stop_at_none' means settling down on the just encountered empty PTE,
> should the above two "if" clauses switch order?  I thought Peter has
> raised this question too, but I'm not seeing a response.
> 
> Regards,
> -jane
> 
> 
>> +        } else if (hugetlb_pte_present_leaf(hpte, pte))
>> +            return 0;
>> +        ret = hugetlb_walk_step(mm, hpte, addr, sz);
>> +    }
>> +
>> +    return ret;
>> +}
>> +
> 
> 

thanks,
-jane