linux-kernel - Re: [PATCH] docs/mm: add VMA locks documentation

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Message-ID: <ZzKrlEAjzZ80M0ik@archie.me>
Date: Tue, 12 Nov 2024 08:12:52 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Matthew Wilcox <willy@...radead.org>,
	Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Suren Baghdasaryan <surenb@...gle.com>,
	Hillf Danton <hdanton@...a.com>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	SeongJae Park <sj@...nel.org>
Subject: Re: [PATCH] docs/mm: add VMA locks documentation

On Fri, Nov 08, 2024 at 12:34:23PM +0000, Lorenzo Stoakes wrote:
> On Fri, Nov 08, 2024 at 12:29:15PM +0000, Lorenzo Stoakes wrote:
> > On Fri, Nov 08, 2024 at 07:25:38PM +0700, Bagas Sanjaya wrote:
> > > On Thu, Nov 07, 2024 at 07:01:37PM +0000, Lorenzo Stoakes wrote:
> > > > +.. note:: In instances where the architecture supports fewer page tables than
> > > > +   five the kernel cleverly 'folds' page table levels, that is skips them within
> > > > +   the logic, regardless we can act as if there were always five.
> > >
> > > What are being skipped if e.g. we only have 3 or 4 page tables?
> > >
> > > Confused...
> >
> > Page table levels, see [0].
> >
> > Typically achieved through stubbing functions out, etc. So in the code you
> > actually write and _conceptually_ there are five levels, only in the final
> > compile you might have things like p4d_present(), p4d_clear() etc. squashed by
> > the compiler into nothing.
> 
> I have updated this note to be a little clearer and to explicitly state
> this. Thanks!

Thanks for clarifying.

-- 
An old man doll... just what I always wanted! - Clara

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