[PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

[Christian König]

Yeah, indeed. But what we could do is to rely on a fixed limit like the 
Intel driver does and I suggested before.

E.g. don't copy anything into a shmemfile when there is only x MB of 
swap space left.

Roger can you test that approach once more with your fix for the OOM 
issues in the page fault handler?

Thanks,
Christian.

Am 31.01.2018 um 09:08 schrieb He, Roger:
> 	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 at lists.freedesktop.org] On Behalf Of Chunming Zhou
> Sent: Wednesday, January 31, 2018 3:15 PM
> To: He, Roger <Hongbo.He at amd.com>; dri-devel at lists.freedesktop.org
> Cc: linux-mm at kvack.org; linux-kernel at vger.kernel.org; Koenig, Christian <Christian.Koenig at amd.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 at amd.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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