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

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Message-ID: <2a1d6a9b-f486-44c8-6d1d-e6bab4dc3ced@linux.dev>
Date: Tue, 23 Jan 2024 10:23:14 +0800
From: Yajun Deng <yajun.deng@...ux.dev>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mmap: introduce vma_range_init()


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.

>>> 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().
>>
> 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.
>