linux-kernel - Re: [PATCH] mm: Remove PMD alignment constraint in execmem

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Message-ID: <aMvf_R4ttLibbnQ1@kernel.org>
Date: Thu, 18 Sep 2025 13:33:33 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Remove PMD alignment constraint in execmem_vmalloc()

On Thu, Sep 18, 2025 at 03:04:53PM +0530, Dev Jain wrote:
> When using vmalloc with VM_ALLOW_HUGE_VMAP flag, it will set the alignment
> to PMD_SIZE internally, if it deems huge mappings to be eligible.
> Therefore, setting the alignment in execmem_vmalloc is redundant. Apart
> from this, it also reduces the probability of allocation in case vmalloc
> fails to allocate hugepages - in the fallback case, vmalloc tries to use
> the original alignment and allocate basepages, which unfortunately will
> again be PMD_SIZE passed over from execmem_vmalloc, thus constraining
> the search for a free space in vmalloc region.
> 
> Therefore, remove this constraint.
> 
> Signed-off-by: Dev Jain <dev.jain@....com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
> mm-selftests pass, but I am not sure if they touch execmem code, and I
> have no experience with this code.
> 
>  mm/execmem.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/mm/execmem.c b/mm/execmem.c
> index 0822305413ec..810a4ba9c924 100644
> --- a/mm/execmem.c
> +++ b/mm/execmem.c
> @@ -38,9 +38,6 @@ static void *execmem_vmalloc(struct execmem_range *range, size_t size,
>  	if (kasan)
>  		vm_flags |= VM_DEFER_KMEMLEAK;
>  
> -	if (vm_flags & VM_ALLOW_HUGE_VMAP)
> -		align = PMD_SIZE;
> -
>  	p = __vmalloc_node_range(size, align, start, end, gfp_flags,
>  				 pgprot, vm_flags, NUMA_NO_NODE,
>  				 __builtin_return_address(0));
> -- 
> 2.30.2
> 

-- 
Sincerely yours,
Mike.