linux-kernel - Re: [PATCH v4 5/7] mm: thp: split huge page to any lower order pages (except order-1).

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Date: Tue, 13 Feb 2024 17:15:08 -0500
From: Zi Yan <ziy@...dia.com>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: "\"Pankaj Raghav (Samsung)\"" <kernel@...kajraghav.com>,
 linux-mm@...ck.org, "\"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>,
 "Michal Koutný" <mkoutny@...e.com>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 "\"Zach O'Keefe\"" <zokeefe@...gle.com>, Hugh Dickins <hughd@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 5/7] mm: thp: split huge page to any lower order pages
 (except order-1).

On 13 Feb 2024, at 17:05, Luis Chamberlain wrote:

> On Tue, Feb 13, 2024 at 04:55:18PM -0500, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>> Order-1 folio is not supported because _deferred_list, which is used by
>> partially mapped folios, is stored in subpage 2 and an order-1 folio only
>> has subpage 0 and 1.
>
> The LBS patches has the patch from Matthew which enables and allowed us
> to successfully test order 1. So this restriction could be dropped if
> that gets merged.

OK. But it only applies to file-backed folios IIUC. Anonymous folios still
cannot be split to order-1.

--
Best Regards,
Yan, Zi

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