linux-kernel - Re: [v1 resend 03/12] mm/thp: zone_device awareness in THP handling code

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Message-ID: <5ba8cf21-60ca-465e-a524-5dd43b9bbc97@nvidia.com>
Date: Sat, 5 Jul 2025 10:14:18 +1000
From: Balbir Singh <balbirs@...dia.com>
To: Mika Penttilä <mpenttil@...hat.com>, linux-mm@...ck.org
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
 Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
 Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Jérôme Glisse
 <jglisse@...hat.com>, Shuah Khan <shuah@...nel.org>,
 David Hildenbrand <david@...hat.com>, Barry Song <baohua@...nel.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ryan Roberts <ryan.roberts@....com>, Matthew Wilcox <willy@...radead.org>,
 Peter Xu <peterx@...hat.com>, Zi Yan <ziy@...dia.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Jane Chu <jane.chu@...cle.com>,
 Alistair Popple <apopple@...dia.com>, Donet Tom <donettom@...ux.ibm.com>
Subject: Re: [v1 resend 03/12] mm/thp: zone_device awareness in THP handling
 code

On 7/4/25 21:10, Mika Penttilä wrote:
>>  /* Racy check whether the huge page can be split */
>> @@ -3543,6 +3594,10 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>  					((mapping || swap_cache) ?
>>  						folio_nr_pages(release) : 0));
>>  
>> +			if (folio_is_device_private(release))
>> +				percpu_ref_get_many(&release->pgmap->ref,
>> +							(1 << new_order) - 1);
> 
> pgmap refcount should not be modified here, count should remain the same after the split also
> 
> 

Good point, let me revisit the accounting

For this patch series, the tests did not catch it since new ref's evaluate to 0

Thanks,
Balbir Singh