linux-kernel - Re: [RFC PATCH 02/12] khugepaged: Generalize alloc_charge

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Message-ID: <AD21C68F-C9BD-4562-B093-06B8493C8143@nvidia.com>
Date: Tue, 17 Dec 2024 08:00:07 -0500
From: Zi Yan <ziy@...dia.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Matthew Wilcox <willy@...radead.org>, Dev Jain <dev.jain@....com>,
 akpm@...ux-foundation.org, david@...hat.com, kirill.shutemov@...ux.intel.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,
 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 02/12] khugepaged: Generalize alloc_charge_folio()

On 17 Dec 2024, at 2:09, Ryan Roberts wrote:

> On 17/12/2024 04:17, Matthew Wilcox wrote:
>> On Mon, Dec 16, 2024 at 10:20:55PM +0530, Dev Jain wrote:
>>>  static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
>>> -			      struct collapse_control *cc)
>>> +			      int order, struct collapse_control *cc)
>>
>> unsigned, surely?
>
> I'm obviously feeling argumentative this morning...
>
> There are plenty of examples of order being signed and unsigned in the code
> base... it's a mess. Certainly the mTHP changes up to now have opted for
> (signed) int. And get_order(), which I would assume to the authority, returns
> (signed) int.
>
> Personally I prefer int for small positive integers; it's more compact. But if
> we're trying to establish a pattern to use unsigned int for all new uses of
> order, that fine too, let's just document it somewhere?

If unsigned is used, I wonder how to handle
for (unsigned order = 9; order >= 0; order--) case. We will need a signed order to
make this work, right?

--
Best Regards,
Yan, Zi