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

[Chunming Zhou]

Discussed with Roger just now, we can try "void si_swapinfo(struct 
sysinfo *val)" function to get the total swap space.

Regards,

David Zhou


On 2018年01月31日 16:12, Christian König wrote:
> 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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