linux-kernel - RE: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

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Message-ID: <MWHPR1201MB0127760D359772D5565BA3EBFDFB0@MWHPR1201MB0127.namprd12.prod.outlook.com>
Date:   Wed, 31 Jan 2018 08:08:15 +0000
From:   "He, Roger" <Hongbo.He@....com>
To:     "Zhou, David(ChunMing)" <David1.Zhou@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Koenig, Christian" <Christian.Koenig@....com>
Subject: RE: [PATCH] mm/swap: add function get_total_swap_pages to expose
 total_swap_pages

	I think this patch isn't need at all. You can directly read total_swap_pages variable in TTM.

Because the variable is not exported by EXPORT_SYMBOL_GPL. So direct using will result in:
"WARNING: "total_swap_pages" [drivers/gpu/drm/ttm/ttm.ko] undefined!".

Thanks
Roger(Hongbo.He)
-----Original Message-----
From: dri-devel [mailto:dri-devel-bounces@...ts.freedesktop.org] On Behalf Of Chunming Zhou
Sent: Wednesday, January 31, 2018 3:15 PM
To: He, Roger <Hongbo.He@....com>; dri-devel@...ts.freedesktop.org
Cc: linux-mm@...ck.org; linux-kernel@...r.kernel.org; Koenig, Christian <Christian.Koenig@....com>
Subject: Re: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

Hi Roger,

I think this patch isn't need at all. You can directly read total_swap_pages variable in TTM. See the comment:

/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */ long total_swap_pages;

there are many places using it directly, you just couldn't change its value. Reading it doesn't need lock.

Regards,

David Zhou

On 2018年01月29日 16:29, Roger He wrote:
> ttm module needs it to determine its internal parameter setting.
>
> Signed-off-by: Roger He <Hongbo.He@....com>
> ---
>   include/linux/swap.h |  6 ++++++
>   mm/swapfile.c        | 15 +++++++++++++++
>   2 files changed, 21 insertions(+)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index c2b8128..708d66f 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -484,6 +484,7 @@ extern int try_to_free_swap(struct page *);
>   struct backing_dev_info;
>   extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
>   extern void exit_swap_address_space(unsigned int type);
> +extern long get_total_swap_pages(void);
>   
>   #else /* CONFIG_SWAP */
>   
> @@ -516,6 +517,11 @@ static inline void show_swap_cache_info(void)
>   {
>   }
>   
> +long get_total_swap_pages(void)
> +{
> +	return 0;
> +}
> +
>   #define free_swap_and_cache(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
>   #define swapcache_prepare(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
>   
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 3074b02..a0062eb 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -98,6 +98,21 @@ static atomic_t proc_poll_event = ATOMIC_INIT(0);
>   
>   atomic_t nr_rotate_swap = ATOMIC_INIT(0);
>   
> +/*
> + * expose this value for others use
> + */
> +long get_total_swap_pages(void)
> +{
> +	long ret;
> +
> +	spin_lock(&swap_lock);
> +	ret = total_swap_pages;
> +	spin_unlock(&swap_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(get_total_swap_pages);
> +
>   static inline unsigned char swap_count(unsigned char ent)
>   {
>   	return ent & ~SWAP_HAS_CACHE;	/* may include SWAP_HAS_CONT flag */

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