Am 30.01.2018 um 08:55 schrieb Michal Hocko:
On Tue 30-01-18 02:56:51, He, Roger wrote:
Hi Michal:
We need a API to tell TTM module the system totally has how many swap
cache. Then TTM module can use it to restrict how many the swap cache
it can use to prevent triggering OOM. For Now we set the threshold of
swap size TTM used as 1/2 * total size and leave the rest for others
use.
Why do you so much memory? Are you going to use TB of memory on large
systems? What about memory hotplug when the memory is added/released?
For graphics and compute applications on GPUs it isn't unusual to use
large amounts of system memory.
Our standard policy in TTM is to allow 50% of system memory to be pinned
for use with GPUs (the hardware can't do page faults).
When that limit is exceeded (or the shrinker callbacks tell us to make
room) we wait for any GPU work to finish and copy buffer content into a
shmem file.
This copy into a shmem file can easily trigger the OOM killer if there
isn't any swap space left and that is something we want to avoid.
So what we want to do is to apply this 50% rule to swap space as well
and deny allocation of buffer objects when it is exceeded.
But get_nr_swap_pages is the only API we can accessed from other
module now. It can't cover the case of the dynamic swap size
increment. I mean: user can use "swapon" to enable new swap file or
swap disk dynamically or "swapoff" to disable swap space.
Exactly. Your scaling configuration based on get_nr_swap_pages or the
available memory simply sounds wrong.
Why? That is pretty much exactly what we are doing with buffer objects
and system memory for years.
Regards,
Christian.
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