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

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Message-ID: <CAMgjq7CtEwBMVz67nA7wL6PryZuTmaOut4yPhUyhQV0xkuc=1Q@mail.gmail.com>
Date: Sat, 6 Sep 2025 21:31:27 +0800
From: Kairui Song <ryncsn@...il.com>
To: Chris Li <chrisl@...nel.org>
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 Sat, Sep 6, 2025 at 8:05 AM Chris Li <chrisl@...nel.org> wrote:
>
> 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"

Thanks, I used some grammar check tools and it seems they are not
perfect with kernel terminologies.

>
> Chris
>