linux-kernel - Re: [PATCH v7 16/20] huge_memory: Add vmf_insert_folio

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Message-ID: <afff4368-9401-4943-b802-1b15bdcf5aaa@redhat.com>
Date: Mon, 10 Feb 2025 19:45:09 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org,
 dan.j.williams@...el.com, linux-mm@...ck.org
Cc: Alison Schofield <alison.schofield@...el.com>, lina@...hilina.net,
 zhang.lyra@...il.com, gerald.schaefer@...ux.ibm.com,
 vishal.l.verma@...el.com, dave.jiang@...el.com, logang@...tatee.com,
 bhelgaas@...gle.com, jack@...e.cz, jgg@...pe.ca, catalin.marinas@....com,
 will@...nel.org, mpe@...erman.id.au, npiggin@...il.com,
 dave.hansen@...ux.intel.com, ira.weiny@...el.com, willy@...radead.org,
 djwong@...nel.org, tytso@....edu, linmiaohe@...wei.com, peterx@...hat.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de,
 david@...morbit.com, chenhuacai@...nel.org, kernel@...0n.name,
 loongarch@...ts.linux.dev
Subject: Re: [PATCH v7 16/20] huge_memory: Add vmf_insert_folio_pmd()

On 04.02.25 23:48, Alistair Popple wrote:
> Currently DAX folio/page reference counts are managed differently to normal
> pages. To allow these to be managed the same as normal pages introduce
> vmf_insert_folio_pmd. This will map the entire PMD-sized folio and take
> references as it would for a normally mapped page.
> 
> This is distinct from the current mechanism, vmf_insert_pfn_pmd, which
> simply inserts a special devmap PMD entry into the page table without
> holding a reference to the page for the mapping.
> 
> It is not currently useful to implement a more generic vmf_insert_folio()
> which selects the correct behaviour based on folio_order(). This is because
> PTE faults require only a subpage of the folio to be PTE mapped rather than
> the entire folio. It would be possible to add this context somewhere but
> callers already need to handle PTE faults and PMD faults separately so a
> more generic function is not useful.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>

Nit: patch subject ;)

> 
> ---
> 
> Changes for v7:
> 
>   - Fix bad pgtable handling for PPC64 (Thanks Dan and Dave)

Is it? ;) insert_pfn_pmd() still doesn't consume a "pgtable_t *"

But maybe I am missing something ...

-- 
Cheers,

David / dhildenb