linux-kernel - Re: [PATCH v5 14/25] rmap: Add support for PUD sized mappings to rmap

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Message-ID: <758c0441-2cb9-41c4-bf70-c5810726779c@redhat.com>
Date: Tue, 7 Jan 2025 12:36:52 +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: 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
Subject: Re: [PATCH v5 14/25] rmap: Add support for PUD sized mappings to rmap

On 07.01.25 04:42, Alistair Popple wrote:
> The rmap doesn't currently support adding a PUD mapping of a
> folio. This patch adds support for entire PUD mappings of folios,
> primarily to allow for more standard refcounting of device DAX
> folios. Currently DAX is the only user of this and it doesn't require
> support for partially mapped PUD-sized folios so we don't support for
> that for now.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> 
> ---
> 
> Changes for v5:
>   - Fixed accounting as suggested by David.
> 
> Changes for v4:
> 
>   - New for v4, split out rmap changes as suggested by David.
> ---
>   include/linux/rmap.h | 15 ++++++++++-
>   mm/rmap.c            | 65 ++++++++++++++++++++++++++++++++++++++++++---
>   2 files changed, 76 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 683a040..7043914 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -192,6 +192,7 @@ typedef int __bitwise rmap_t;
>   enum rmap_level {
>   	RMAP_LEVEL_PTE = 0,
>   	RMAP_LEVEL_PMD,
> +	RMAP_LEVEL_PUD,
>   };
>   
>   static inline void __folio_rmap_sanity_checks(const struct folio *folio,
> @@ -228,6 +229,14 @@ static inline void __folio_rmap_sanity_checks(const struct folio *folio,
>   		VM_WARN_ON_FOLIO(folio_nr_pages(folio) != HPAGE_PMD_NR, folio);
>   		VM_WARN_ON_FOLIO(nr_pages != HPAGE_PMD_NR, folio);
>   		break;
> +	case RMAP_LEVEL_PUD:
> +		/*
> +		 * Assume that we are creating * a single "entire" mapping of the
> +		 * folio.

Misplaced " *", can likely be fixed up when applying.

Apart from that LGTM

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb