linux-kernel - Re: [PATCH 4/4] mm: Optimise vmf_anon_prepare() for VMAs without an anon

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Date: Fri, 26 Apr 2024 19:36:31 +0200
From: David Hildenbrand <david@...hat.com>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Suren Baghdasaryan <surenb@...gle.com>, Peter Xu <peterx@...hat.com>,
 Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 4/4] mm: Optimise vmf_anon_prepare() for VMAs without an
 anon_vma

On 26.04.24 16:45, Matthew Wilcox (Oracle) wrote:
> If the mmap_lock can be taken for read, we can call __anon_vma_prepare()
> while holding it, saving ourselves a trip back through the fault handler.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Reviewed-by: Jann Horn <jannh@...gle.com>
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>   mm/memory.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 7dc112d3a7e4..b5453b86ec4b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3232,16 +3232,21 @@ static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
>   vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
>   {
>   	struct vm_area_struct *vma = vmf->vma;
> +	vm_fault_t ret = 0;
>   
>   	if (likely(vma->anon_vma))
>   		return 0;
>   	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> -		vma_end_read(vma);
> -		return VM_FAULT_RETRY;
> +		if (!mmap_read_trylock(vma->vm_mm)) {
> +			vma_end_read(vma);
> +			return VM_FAULT_RETRY;
> +		}
>   	}
>   	if (__anon_vma_prepare(vma))
> -		return VM_FAULT_OOM;
> -	return 0;
> +		ret = VM_FAULT_OOM;
> +	if (vmf->flags & FAULT_FLAG_VMA_LOCK)
> +		mmap_read_unlock(vma->vm_mm);
> +	return ret;
>   }
>   
>   /*

Fancy

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb