linux-kernel - Re: [PATCH v2 1/5] mm/hugetlb: fix races when looking up a CONT-PTE size hugetlb page

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Date:   Thu, 25 Aug 2022 09:10:41 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Cc:     akpm@...ux-foundation.org, songmuchun@...edance.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] mm/hugetlb: fix races when looking up a CONT-PTE
 size hugetlb page

>> +		/*
>> +		 * try_grab_page() should always succeed here, because we hold
>> +		 * the ptl lock and have verified pte_present().
>> +		 */
>> +		if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
>> +			page = NULL;
>> +			goto out;
>> +		}
>> +	} else {
> 
> Should add FOLL_MIGRATION validation before waiting a migration entry.

We really only need FOLL_MIGRATION for KSM. As hugetlb pages cannot be
KSM pages, we don't need this.

Actually, I do have patches in the works that rip out FOLL_MIGRATION
completely by adjusting KSM code.

So let's try to not add dead code (although it would make sense for
feature completeness as is -- but then, FOLL_MIGRATION really needs to go).

-- 
Thanks,

David / dhildenb