Re: [PATCH RFC v2] mm: introduce copy_mc_highpages() and batch copy in folio_mc_copy()

["David Hildenbrand (Arm)" <david@kernel.org>]

>> +}
>> +#else
>> +
>> +#define COPY_MC_PAGES_NON_PREEMPT_BATCH		1
> 
> I would suggest that perhaps this should be the fallback for non-preemptible
> models. But it gets a little weird with PREEMPT_DYNAMIC I think?

Why can't we just use PROCESS_PAGES_NON_PREEMPT_BATCH where we have similar
handling already?

> 
>> +
>> +static inline int copy_mc_highpages(struct page *to, struct page *from,
>> +		unsigned long nr_pages)
>> +{
>> +	unsigned long i;
>> +
>> +	for (i = 0; i < nr_pages; i++)
>> +		if (copy_mc_highpage(to + i, from + i))
>> +			return -EHWPOISON;
>> +	return 0;
>> +}
>> +#endif
>> +
>>  static inline void memcpy_page(struct page *dst_page, size_t dst_off,
>>  			       struct page *src_page, size_t src_off,
>>  			       size_t len)
>> diff --git a/mm/util.c b/mm/util.c
>> index 7f374bb8bf36..5015cfdfeaa5 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -763,13 +763,23 @@ EXPORT_SYMBOL(folio_copy);
>>  
>>  int folio_mc_copy(struct folio *dst, struct folio *src)
>>  {
>> -	long nr = folio_nr_pages(src);
>> -	long i = 0;
>> +	const unsigned long nr_pages = folio_nr_pages(src);
>> +	/*
>> +	 * Copy the largest extent possible to allow for architecture specific
>> +	 * extent based optimizations. copy_mc_highpages() does not call
>> +	 * cond_resched(), so limit the unit size when running under
>> +	 * non-preemptible scheduling models.
>> +	 */
>> +	const unsigned long unit = preempt_model_preemptible() ?
>> +				   nr_pages : COPY_MC_PAGES_NON_PREEMPT_BATCH;
> 
> See? now mm is aware of preemption models! eww!

Yeah, we have that in clear_contig_highpages() already, which is getting
replicated here for copying instead of zeroing.

-- 
Cheers,

David