linux-kernel - Re: [PATCH v2 01/15] docs/mm: add document for swap table

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Message-ID: <CAF8kJuMsGGtOuPpDwFKq0sNhX7HKbQWWK31uWpqeqW-RGTo-0A@mail.gmail.com>
Date: Fri, 5 Sep 2025 16:58:00 -0700
From: Chris Li <chrisl@...nel.org>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>, Barry Song <baohua@...nel.org>, 
	Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>, 
	Kemeng Shi <shikemeng@...weicloud.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Ying Huang <ying.huang@...ux.alibaba.com>, Johannes Weiner <hannes@...xchg.org>, 
	David Hildenbrand <david@...hat.com>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/15] docs/mm: add document for swap table

On Fri, Sep 5, 2025 at 12:14 PM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> From: Chris Li <chrisl@...nel.org>
>
> Swap table is the new swap cache.
>
> Signed-off-by: Chris Li <chrisl@...nel.org>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>  Documentation/mm/swap-table.rst | 72 +++++++++++++++++++++++++++++++++
>  MAINTAINERS                     |  1 +
>  2 files changed, 73 insertions(+)
>  create mode 100644 Documentation/mm/swap-table.rst
>
> diff --git a/Documentation/mm/swap-table.rst b/Documentation/mm/swap-table.rst
> new file mode 100644
> index 000000000000..929cd91aa984
> --- /dev/null
> +++ b/Documentation/mm/swap-table.rst
> @@ -0,0 +1,72 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +:Author: Chris Li <chrisl@...nel.org>, Kairui Song <kasong@...cent.com>
> +
> +==========
> +Swap Table
> +==========
> +
> +Swap table implements swap cache as a per-cluster swap cache value array.
> +
> +Swap Entry
> +----------
> +
> +A swap entry contains the information required to serve the anonymous page
> +fault.
> +
> +Swap entry is encoded as two parts: swap type and swap offset.
> +
> +The swap type indicates which swap device to use.
> +The swap offset is the offset of the swap file to read the page data from.
> +
> +Swap Cache
> +----------
> +
> +Swap cache is a map to look up folios using swap entry as the key. The result
> +value can have three possible types depending on which stage of this swap entry
> +was in.
> +
> +1. NULL: This swap entry is not used.
> +
> +2. folio: A folio has been allocated and bound to this swap entry. This is
> +   the transient state of swap out or swap in. The folio data can be in
> +   the folio or swap file, or both.
> +
> +3. shadow: The shadow contains the working set information of the swap

I just noticed a typo here, should be "swapped out page"

> +   outed folio. This is the normal state for a swap outed page.

Same here. "swap outed page" -> "swapped out page"

Chris