Re: [PATCH 11/41] drm/i915: Introduce an internal allocator for disposable private objects

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 14/10/2016 14:53, Chris Wilson wrote:
> On Fri, Oct 14, 2016 at 02:44:00PM +0100, Tvrtko Ursulin wrote:
>> On 14/10/2016 13:54, Chris Wilson wrote:
>>> On Fri, Oct 14, 2016 at 01:42:35PM +0100, Tvrtko Ursulin wrote:
>>>> On 14/10/2016 13:18, Chris Wilson wrote:
>>>>> +	gfp = GFP_KERNEL | __GFP_HIGHMEM | __GFP_RECLAIMABLE;
>>>>> +	if (IS_CRESTLINE(i915) || IS_BROADWATER(i915)) {
>>>>> +		/* 965gm cannot relocate objects above 4GiB. */
>>>>> +		gfp &= ~__GFP_HIGHMEM;
>>>>> +		gfp |= __GFP_DMA32;
>>>>> +	}
>>>>> +
>>>>> +	do {
>>>>> +		int order = min(fls(npages) - 1, max_order);
>>>> I still have reservations on going back to max_order when previous
>>>> chunks required an order decrease. Size of the object is unbound
>>>> since it is indirectly controlled by userspace, correct? How about
>>>> decreasing the max_order on every repeated order decrease, following
>>>> failed order allocation?
>>>>> +		struct page *page;
>>>>> +
>>>>> +		do {
>>>>> +			page = alloc_pages(gfp | (order ? QUIET : 0), order);
>>>>> +			if (page)
>>>>> +				break;
>>>>> +			if (!order--)
>>>>> +				goto err;
>>> Like:
>>> 			/* Limit future allocations as well */
>>> 			max_order = order;
>>>
>>>>> +		} while (1);
>>> We do pass NORETRY | NOWARN for the higher order allocations, so it
>>> shouldn't be as bad it seems?
>> I don't know for sure without looking into the implementation
>> details. But I assumed even with NORETRY it does some extra work to
>> try and free up the space. And if it fails, and we ask for it again,
>> it is just doing that extra work for nothing. Because within a
>> single allocation it sounds unlikely that something would change so
>> dramatically that it would start working.
> iirc, NORETRY means abort after failure. In effect, it does
> 2 attempts from the freelist, a direct reclaim, and may then repeat
> if the task's allowed set of nodes were concurrently changed.

Do you think it makes sense doing all that after it started failing, 
within our single get_pages allocation?

Regards,

Tvrtko

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