On 8 Jun 2026, at 16:33, Michael S. Tsirkin wrote:
> On Mon, Jun 08, 2026 at 04:21:08PM -0400, Zi Yan wrote:
>> On 8 Jun 2026, at 15:59, Gregory Price wrote:
>>
>>> On Mon, Jun 08, 2026 at 02:04:28PM +0100, Matthew Wilcox wrote:
>>>> On Mon, Jun 08, 2026 at 12:06:35PM +0100, Lorenzo Stoakes wrote:
>>>>> But instead of overloading user_addr to indicate all kinds of things,
>>>>> instead
>>>>> make life easier by actually breaking things out.
>>>>>
>>>>> Like:
>>>>>
>>>>> enum alloc_context_type {
>>>>> KERNEL_ALLOCATION,
>>>>> USER_MAPPED_ALLOCATION,
>>>>> USER_UNMAPPED_ALLOCATION, // Maybe? Do we ever?
>>>>> /* Perhaps some other states we want to encode? */
>>>>> };
>>>>>
>>>>> struct alloc_context {
>>>>> ...
>>>>>
>>>>> enum alloc_context_type type;
>>>>> unsigned long user_addr; // Only set if type == USER_ALLOCATION
>>>>>
>>>>> // Maybe something suggesting context or whether we init before in some
>>>>> // cases?
>>>>> };
>>>>
>>>> Ugh, please, no. As I suggested last time I commented on this
>>>> trainwreck of a series, lift the zeroing functionality from
>>>> alloc_frozen_pages() into its callers.
>>>
>>> This sort of just implies writing the "alloc_frozen_zeroed_pages()"
>>> wrapper that does the zeroing at the end before return, and then killing
>>> the post hook nonsense associated with it in the first place.
>>
>> This means it is going to be a multi-step optimization. This is probably
>> step 1.
>>
>>>
>>> None of this resolves the user address annoyance which is needed on some
>>> archs for cache flushing. Whether anyone agrees that the page allocator
>>> should be responsible for this particular operation - open debate.
>>
>> This is probably step 2. But does the virtio use case apply to these
>> archs? Does the performance matter for them? If not, maybe this part can
>> be left as a TODO.
>>
>>
>> Best Regards,
>> Yan, Zi
>
> I doubt it. But I don't get what's proposed, the code that we
> have to modify is arch independent?
Change user_alloc_needs_zeroing() to only check address aliasing even
if that can cause double zeroing for virtio.
Best Regards,
Yan, Zi
