From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Kiryl Shutsemau <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@meta.com, Zi Yan <ziy@nvidia.com>,
"Liam R . Howlett" <liam@infradead.org>,
Nico Pache <nico.pache@linux.dev>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>, Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Vlastimil Babka <vbabka@kernel.org>, Jann Horn <jannh@google.com>
Subject: Re: [PATCH 05/12] mm/collapse: state what a collapse may do in the policy
Date: Tue, 8 Sep 2026 09:48:17 +0800 [thread overview]
Message-ID: <04df803b-b168-41b7-b394-1071e002e3bc@linux.alibaba.com> (raw)
In-Reply-To: <ap6XERs2j7e1lZCU@thinkstation>
On 9/7/26 6:56 PM, Kiryl Shutsemau wrote:
> On Mon, Sep 07, 2026 at 05:05:19PM +0800, Baolin Wang wrote:
>>> +/* What a collapse is allowed to do, decided by the caller that asks for it */
>>> +struct collapse_policy {
>>> + /* Limits, stated per PMD; HPAGE_PMD_NR means "no limit" */
>>> + unsigned int max_ptes_none;
>>> + unsigned int max_ptes_swap;
>>> + unsigned int max_ptes_shared;
>>> +
>>> + /*
>>> + * Hold a sub-PMD window to a stricter rule than a PMD: no swapped-out
>>> + * and no shared PTEs at all, and max_ptes_none as
>>> + * collapse_max_ptes_none() scales it.
>>> + */
>>> + bool strict_sub_pmd;
>>
>> This is a bit confusing to me. Actually, the check for mTHP collapse is
>> stricter.
>>
>> How about naming it 'allow_mthp_collapse'? That way we can keep the most
>> original comments for the collapse_max_ptes_xxx() functions, which is
>> clearer to me.
>>
>> If others have a better name, please ignore my comment.
>
> I would rather keep strict_sub_pmd.
>
> Which orders a caller asks for is already decided elsewhere:
> collapse_possible_orders() hands khugepaged every anonymous order and
> MADV_COLLAPSE the PMD order only, from tva_type.
>
> A flag called allow_mthp_collapse next to that would read as
> a second place deciding the same thing, and flipping it would not change
> which orders get collapsed. What it does change is how a sub-PMD window
> is judged once one is asked for, and it is read at exactly the three
> places that judge one.
>
> I will do:
>
> /* Take no swapped-out or shared PTE into a sub-PMD collapse */
> bool strict_sub_pmd;
OK. Fair enough. Thanks.
next prev parent reply other threads:[~2026-09-08 1:48 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-04 15:10 [PATCH 00/12] mm/collapse: separate a collapse from its callers Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 01/12] mm/khugepaged: drop redundant mm_struct pin in madvise_collapse() Kiryl Shutsemau
2026-09-04 15:58 ` Zi Yan
2026-09-07 7:33 ` Baolin Wang
2026-09-04 15:10 ` [PATCH 02/12] mm/khugepaged: count collapses where khugepaged makes them Kiryl Shutsemau
2026-09-05 2:25 ` Zi Yan
2026-09-07 7:40 ` Baolin Wang
2026-09-04 15:10 ` [PATCH 03/12] mm/khugepaged: rename mthp_present_ptes bitmap to eligible_ptes Kiryl Shutsemau
2026-09-05 2:28 ` Zi Yan
2026-09-07 7:54 ` Baolin Wang
2026-09-07 10:35 ` Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 04/12] mm/collapse: add collapse.h for the collapse interface Kiryl Shutsemau
2026-09-05 2:36 ` Zi Yan
2026-09-07 10:41 ` Kiryl Shutsemau
2026-09-07 8:04 ` Baolin Wang
2026-09-04 15:10 ` [PATCH 05/12] mm/collapse: state what a collapse may do in the policy Kiryl Shutsemau
2026-09-05 2:44 ` Zi Yan
2026-09-07 10:49 ` Kiryl Shutsemau
2026-09-07 19:40 ` Zi Yan
2026-09-07 9:05 ` Baolin Wang
2026-09-07 10:56 ` Kiryl Shutsemau
2026-09-08 1:48 ` Baolin Wang [this message]
2026-09-04 15:10 ` [PATCH 06/12] mm/collapse: drop the collapse_possible() wrapper Kiryl Shutsemau
2026-09-05 2:45 ` Zi Yan
2026-09-07 8:28 ` Baolin Wang
2026-09-04 15:10 ` [PATCH 07/12] mm/collapse: name the per-table scan reset for what it resets Kiryl Shutsemau
2026-09-05 18:05 ` Zi Yan
2026-09-07 8:31 ` Baolin Wang
2026-09-04 15:10 ` [PATCH 08/12] mm/collapse: separate scanning a PTE table from collapsing it Kiryl Shutsemau
2026-09-06 2:30 ` Zi Yan
2026-09-07 11:34 ` Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 09/12] mm/collapse: open-code collapse_single_pmd() in its two callers Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 10/12] mm/collapse: work out the orders a VMA allows once per VMA Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 11/12] mm/collapse: declare the collapse interface in collapse.h Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 12/12] mm/collapse: implement MADV_COLLAPSE in madvise.c Kiryl Shutsemau
2026-09-06 0:23 ` [PATCH 00/12] mm/collapse: separate a collapse from its callers Andrew Morton
2026-09-07 10:28 ` Kiryl Shutsemau
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