linux-kernel - Re: [RFC PATCH 05/12] khugepaged: Generalize __collapse_huge_page

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Message-ID: <82c8712b-b7c3-4b58-8b29-dbc436d885be@arm.com>
Date: Tue, 17 Dec 2024 12:11:42 +0530
From: Dev Jain <dev.jain@....com>
To: Matthew Wilcox <willy@...radead.org>, g@...per.infradead.org
Cc: akpm@...ux-foundation.org, david@...hat.com,
 kirill.shutemov@...ux.intel.com, ryan.roberts@....com,
 anshuman.khandual@....com, catalin.marinas@....com, cl@...two.org,
 vbabka@...e.cz, mhocko@...e.com, apopple@...dia.com,
 dave.hansen@...ux.intel.com, will@...nel.org, baohua@...nel.org,
 jack@...e.cz, srivatsa@...il.mit.edu, haowenchao22@...il.com,
 hughd@...gle.com, aneesh.kumar@...nel.org, yang@...amperecomputing.com,
 peterx@...hat.com, ioworker0@...il.com, wangkefeng.wang@...wei.com,
 ziy@...dia.com, jglisse@...gle.com, surenb@...gle.com,
 vishal.moola@...il.com, zokeefe@...gle.com, zhengqi.arch@...edance.com,
 jhubbard@...dia.com, 21cnbao@...il.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 05/12] khugepaged: Generalize
 __collapse_huge_page_isolate()


On 17/12/24 10:02 am, Matthew Wilcox wrote:
> On Mon, Dec 16, 2024 at 10:20:58PM +0530, Dev Jain wrote:
>>   {
>> -	struct page *page = NULL;
>> -	struct folio *folio = NULL;
>> -	pte_t *_pte;
>> +	unsigned int max_ptes_shared = khugepaged_max_ptes_shared >> (HPAGE_PMD_ORDER - order);
>> +	unsigned int max_ptes_none = khugepaged_max_ptes_none >> (HPAGE_PMD_ORDER - order);
>>   	int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
>> +	struct folio *folio = NULL;
>> +	struct page *page = NULL;
> why are you moving variables around unnecessarily?

In a previous work, I moved code around and David noted to arrange the declarations
in reverse Xmas tree order. I guess (?) that was not spoiling git history, so if
this feels like that, I will revert.

>
>>   	bool writable = false;
>> +	pte_t *_pte;
>>   
>> -	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
>> +
>> +	for (_pte = pte; _pte < pte + (1UL << order);
> spurious blank line

My bad

>
>
> also you might first want to finish off the page->folio conversion in
> this function first; we have a vm_normal_folio() now.

I did not add any code before we derive the folio...I'm sorry, I don't get what you mean...