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

[Chris Li <chrisl@kernel.org>]

On Thu, Sep 18, 2025 at 1:59 AM Barry Song <21cnbao@gmail.com> wrote:
>
> On Thu, Sep 18, 2025 at 3:03 PM Chris Li <chrisl@kernel.org> wrote:
> >
> > Hi Barry,
> >
> > How about this:
> >
> > A swap table stores one cluster worth of swap cache values, which is
> > exactly one page table page on most morden 64 bit systems. This is not
> > coincidental because the cluster size is determined by the huge page size.
>
> I’d phrase it as “PMD huge page,” since we also have “PUD huge page.”

Good point. Will do.

>
> > The swap table is holding an array of pointers, which have the same
> > size as the PTE. The size of the swap table should match the page table
> > page.
> >
>
> I’m not entirely sure what you mean by “page table page.”

The page that gets pointed by the page table, or the page that holds the PTE.

> My understanding is that you’re saying:
> The swap table contains an array of pointers, each the same size as a PTE,
> so its total size typically matches a PTE page table—one page on modern
> 64-bit systems.

That sounds good. Thanks for the suggestion.
I take your suggestion with some small modifications, mostly to
clarify the total size is the total size of one cluster of swap
tables. The total size of all swap tables in a swap file is much
bigger.

How about this:

A swap table is an array of pointers. Each pointer is the same size as a PTE.
The size of a swap table for one swap cluster typically matches a PTE
page table,
which is one page on modern 64-bit systems.

Chris