linux-kernel - Re: [PATCH v7 10/17] mm: uninline the main body of vma_start

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Message-ID: <0d36fd53-b817-4bbd-ae38-af094bd301df@suse.cz>
Date: Tue, 7 Jan 2025 18:35:45 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: peterz@...radead.org, willy@...radead.org, liam.howlett@...cle.com,
 lorenzo.stoakes@...cle.com, mhocko@...e.com, hannes@...xchg.org,
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 david@...hat.com, peterx@...hat.com, oleg@...hat.com, dave@...olabs.net,
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Subject: Re: [PATCH v7 10/17] mm: uninline the main body of vma_start_write()

On 12/26/24 18:07, Suren Baghdasaryan wrote:
> vma_start_write() is used in many places and will grow in size very soon.
> It is not used in performance critical paths and uninlining it should
> limit the future code size growth.
> No functional changes.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6328,6 +6328,20 @@ struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm,
>  #endif
>  
>  #ifdef CONFIG_PER_VMA_LOCK
> +void __vma_start_write(struct vm_area_struct *vma, unsigned int mm_lock_seq)
> +{
> +	down_write(&vma->vm_lock.lock);
> +	/*
> +	 * We should use WRITE_ONCE() here because we can have concurrent reads
> +	 * from the early lockless pessimistic check in vma_start_read().
> +	 * We don't really care about the correctness of that early check, but
> +	 * we should use WRITE_ONCE() for cleanliness and to keep KCSAN happy.
> +	 */
> +	WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq);
> +	up_write(&vma->vm_lock.lock);
> +}
> +EXPORT_SYMBOL_GPL(__vma_start_write);

Do any modules need it? If not we shouldn't export.

>  /*
>   * Lookup and lock a VMA under RCU protection. Returned VMA is guaranteed to be
>   * stable and not isolated. If the VMA is not found or is being modified the