linux-kernel - Re: [PATCH v3 5/7] mm/vmalloc: skip the uninitilized vmalloc areas

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Date:   Mon, 16 Jan 2023 12:44:42 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, urezki@...il.com,
        lstoakes@...il.com, stephen.s.brennan@...cle.com,
        willy@...radead.org, akpm@...ux-foundation.org, hch@...radead.org
Subject: Re: [PATCH v3 5/7] mm/vmalloc: skip the uninitilized vmalloc areas

On Fri, Jan 13, 2023 at 11:19:19AM +0800, Baoquan He wrote:
> For areas allocated via vmalloc_xxx() APIs, it searches for unmapped area
> to reserve and allocates new pages to map into, please see function
> __vmalloc_node_range(). During the process, flag VM_UNINITIALIZED is set
> in vm->flags to indicate that the pages allocation and mapping haven't
> been done, until clear_vm_uninitialized_flag() is called to clear it.
> 
> For this kind of area, if VM_UNINITIALIZED is still set, let's ignore
> it in vread() because pages newly allocated and being mapped in that
> area only contains zero data. reading them out by aligned_vread() is
> wasting time.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  mm/vmalloc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 4a10b3b692fa..dbcdcad2276b 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3660,6 +3660,11 @@ long vread(char *buf, char *addr, unsigned long count)
>  		if (!vm && !flags)
>  			continue;
>  
> +		if (vm && (vm->flags & VM_UNINITIALIZED))
> +			continue;
> +		/* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
> +		smp_rmb();
> +
>  		vaddr = (char *) va->va_start;
>  		size = vm ? get_vm_area_size(vm) : va_size(va);
>  
> -- 
> 2.34.1
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>

--
Uladzislau Rezki