linux-kernel - Re: [PATCH 1/2] mm/huge_memory: check new folio order when split a folio

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Date: Thu, 07 Mar 2024 15:09:40 -0500
From: Zi Yan <ziy@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, Dan Carpenter <dan.carpenter@...aro.org>,
 "\"Pankaj Raghav (Samsung)\"" <kernel@...kajraghav.com>,
 "\"Matthew Wilcox (Oracle)\"" <willy@...radead.org>,
 David Hildenbrand <david@...hat.com>, Yang Shi <shy828301@...il.com>,
 Yu Zhao <yuzhao@...gle.com>,
 "\"Kirill A . Shutemov\"" <kirill.shutemov@...ux.intel.com>,
 Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/huge_memory: check new folio order when split a
 folio

On 7 Mar 2024, at 15:02, Andrew Morton wrote:

> On Thu,  7 Mar 2024 13:18:53 -0500 Zi Yan <zi.yan@...t.com> wrote:
>
>> From: Zi Yan <ziy@...dia.com>
>>
>> A folio can only be split into lower orders. Check new_order to make sure
>> it is smaller than input folio order.
>
> It isn't clear what's being fixed here.  Presumably something is
> passing in such folios, but what and where and why and what are the
> effects?
>
> Might it be that these folios are being caused by the debugfs
> interface?  Or something else?

Since there is no new_order checks in debugfs before, any
new_order can be passed via debugfs into
split_huge_page_to_list_to_order().

I did not explicitly mention it here as the debugfs is added in
the commit after the Fixes one.

>
> So I'll add it, but I do think more information and context would
> improve the patch, please.  Suitable Reported-by:, Closes: and Link:
> tags, perhaps.

--
Best Regards,
Yan, Zi

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