Re: [PATCHv2 6/7] x86/mm: Provide helpers for unaccepted memory

[Dave Hansen <dave.hansen@intel.com>]

On 1/11/22 03:33, Kirill A. Shutemov wrote:
> Core-mm requires few helpers to support unaccepted memory:
> 
>   - accept_memory() checks the range of addresses against the bitmap and
>     accept memory if needed;
> 
>   - maybe_set_page_offline() checks the bitmap and marks a page with
>     PageOffline() if memory acceptance required on the first
>     allocation of the page.
> 
>   - accept_and_clear_page_offline() accepts memory for the page and clears
>     PageOffline().
> 
...
> +void accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	unsigned long flags;
> +	if (!boot_params.unaccepted_memory)
> +		return;
> +
> +	spin_lock_irqsave(&unaccepted_memory_lock, flags);
> +	__accept_memory(start, end);
> +	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
> +}

Not a big deal, but please cc me on all the patches in the series.  This 
is called from the core mm patches which I wasn't cc'd on.

This also isn't obvious, but this introduces a new, global lock into the 
fast path of the page allocator and holds it for extended periods of 
time.  It won't be taken any more once all memory is accepted, but you 
can sure bet that it will be noticeable until that happens.

*PLEASE* document this.  It needs changelog and probably code comments.