linux-kernel - Re: [PATCH v10 07/13] khugepaged: skip collapsing mTHP to smaller orders

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <8e11042c-0e7c-41ac-8da1-b6c6a1c1dbf6@arm.com>
Date: Thu, 21 Aug 2025 18:03:52 +0530
From: Dev Jain <dev.jain@....com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Nico Pache <npache@...hat.com>
Cc: linux-mm@...ck.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 david@...hat.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
 Liam.Howlett@...cle.com, ryan.roberts@....com, corbet@....net,
 rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 akpm@...ux-foundation.org, baohua@...nel.org, willy@...radead.org,
 peterx@...hat.com, wangkefeng.wang@...wei.com, usamaarif642@...il.com,
 sunnanyong@...wei.com, vishal.moola@...il.com,
 thomas.hellstrom@...ux.intel.com, yang@...amperecomputing.com,
 kirill.shutemov@...ux.intel.com, aarcange@...hat.com, raquini@...hat.com,
 anshuman.khandual@....com, catalin.marinas@....com, tiwai@...e.de,
 will@...nel.org, dave.hansen@...ux.intel.com, jack@...e.cz, cl@...two.org,
 jglisse@...gle.com, surenb@...gle.com, zokeefe@...gle.com,
 hannes@...xchg.org, rientjes@...gle.com, mhocko@...e.com,
 rdunlap@...radead.org, hughd@...gle.com
Subject: Re: [PATCH v10 07/13] khugepaged: skip collapsing mTHP to smaller
 orders


On 21/08/25 5:35 pm, Lorenzo Stoakes wrote:
>
>
>> ---
>>   mm/khugepaged.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 1ad7e00d3fd6..6a4cf7e4a7cc 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -611,6 +611,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>>   		folio = page_folio(page);
>>   		VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);
>>
>> +		/*
>> +		 * TODO: In some cases of partially-mapped folios, we'd actually
>> +		 * want to collapse.
>> +		 */
> Not a fan of adding todo's in code, they have a habit of being left forever. I'd
> maybe put a more written  out comment something similar to the commit message.

I had suggested to add in https://lore.kernel.org/all/20250211111326.14295-10-dev.jain@arm.com/
from the get go, but then we decided to leave it for later. So rest assured this TODO won't
be left forever : )

>
>> +		if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) {
>> +			result = SCAN_PTE_MAPPED_HUGEPAGE;
>> +			goto out;
>> +		}
>> +
>>   		/* See collapse_scan_pmd(). */
>>   		if (folio_maybe_mapped_shared(folio)) {
>>   			++shared;
>> --
>> 2.50.1
>>