linux-kernel - Re: [PATCH] mm/mmap: introduce vma_range

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Message-ID: <20240123031906.pwbjuzdpl6hqiptj@revolver>
Date: Mon, 22 Jan 2024 22:19:06 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Yajun Deng <yajun.deng@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mmap: introduce vma_range_init()

* Yajun Deng <yajun.deng@...ux.dev> [240122 21:23]:
> 
> On 2024/1/23 08:18, Liam R. Howlett wrote:
> > * Andrew Morton <akpm@...ux-foundation.org> [240122 18:40]:
> > > On Mon, 22 Jan 2024 17:00:31 -0500 "Liam R. Howlett" <Liam.Howlett@...cle.com> wrote:
> > > 
> > > > * Yajun Deng <yajun.deng@...ux.dev> [240110 21:15]:
> > > > > There is a lot of code needs to set the range of vma, introduce
> > > > > vma_range_init() to initialize the range of vma.
> > > > > 
> > > > > Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> > > > > ---
> > > > >   include/linux/mm.h |  9 +++++++++
> > > > >   mm/mmap.c          | 29 +++++++----------------------
> > > > >   2 files changed, 16 insertions(+), 22 deletions(-)
> > > > This isn't a whole lot of code, are there others?  We're losing code
> > > > clarity in favour of saving 6 lines?
> > > > 
> > > Oh.  I thought it was a nice cleanup which made things more clear.
> > I'm not totally against it; that's why I suggested the changes below. I
> > think a name change would go a long way for clarity. It's not as much as
> > I though it would be though.
> > 
> > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > > > index f5a97dec5169..abb4534be3cc 100644
> > > > > --- a/include/linux/mm.h
> > > > > +++ b/include/linux/mm.h
> > > > > @@ -3516,6 +3516,15 @@ static inline bool range_in_vma(struct vm_area_struct *vma,
> > > > >   	return (vma && vma->vm_start <= start && end <= vma->vm_end);
> > > > >   }
> > > > > +static inline void vma_range_init(struct vm_area_struct *vma,
> > > > Any reason this can't be in mm/internal.h ?
> > > That would be good.
> > One other thing, do we trust this to be inlined correctly by the
> > compiler or should this be __always_inline?  I'd expect it to be okay as
> > it is, but I've been proven wrong in a perf trace before..
> > 
> 
> Okay, I would take __always_inline and put it in mm/internal.h in v2.

I'm not confident in this suggestion as the rest.
Please rename the function when you move it.

> 
> > > > vma_range_set(), vma_set_range(), or just vma_range() might be a better
> > > > name?  My thinking is that some of these are actually modifying the vma
> > > > and not just initializing it, right?
> > > I'd vote for vma_set_range().
                      ^  This part, use vma_set_range() please.

> > Using vma_set_range() leaves vma_range() or vma_size(), which could be
> > added for the calculations of vma->vm_end - vma->vm_start.  Davidlohr
> > suggested such a beast a few years ago, but that one would need to live
> > in the include/linux/mm.h as it occurs a lot more.
> > 
> > $ git grep "vma->vm_end - vma->vm_start" | wc -l
> > 198
> > 
> > .. for just those named vma.
> > 
>