linux-kernel - Re: [PATCH v4 01/15] docs/mm: add document for swap table

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Message-ID: <CAGsJ_4xTPJo7+kCkkiZhn8b7xjH7yXeJ2XPoXeoJm+XwJB_o9A@mail.gmail.com>
Date: Thu, 18 Sep 2025 07:50:34 +0800
From: Barry Song <21cnbao@...il.com>
To: Chris Li <chrisl@...nel.org>
Cc: Kairui Song <ryncsn@...il.com>, linux-mm@...ck.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Matthew Wilcox <willy@...radead.org>, 
	Hugh Dickins <hughd@...gle.com>, 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, Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH v4 01/15] docs/mm: add document for swap table

> Perhaps you could describe the swap table as similar to a PTE page table
> representing the swap cache mapping.
> That is correct for most 32-bit and 64-bit systems,
> but not for every machine.
>
> The only exception is a 32-bit system with a 64-bit physical address
> (Large Physical Address Extension, LPAE), which uses a 4 KB PTE table
> but a 2 KB swap table because the pointer is 32 bit while each page
> table entry is 64 bit.
>
> Maybe we can simply say that the number of entries in the swap table
> is the same as in a PTE page table?

BTW, as Kairui mentioned, you plan to store the PFN instead of a
pointer in phase 2.

I wonder whether we need to switch to atomic64_t on systems where the
physical address is 64 bit but the virtual address is 32 bit :-)

Thanks
Barry