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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANeU7QkKS+1TvCRkJUcWQo_emyDJ-q261SfjKoPuEfPG3Pbifw@mail.gmail.com>
Date: Wed, 17 Sep 2025 21:50:53 -0700
From: Chris Li <chrisl@...nel.org>
To: Barry Song <21cnbao@...il.com>
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

On Wed, Sep 17, 2025 at 4:50 PM Barry Song <21cnbao@...il.com> wrote:
>
> > 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.

Yes, let's update the document then and only then. Otherwise the
document will be mismatching the code and confuse the reader.

>
> 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 :-)

It is possible we need 64 bit for the swap cache anyway for other
reasons when we get into the later phases. Again, let's deal with it
later.

Chris