On 2022-04-28 12:54:14 [+0200], Fabio M. De Francesco wrote: > No, it's not sufficient because Matthew Wilcox said that something like "It > is the counterpart of kmap_atomic() for unmapping" (or anything similar) is > _not_ what he wants to see. > > Furthermore, a large part of this text has been written by him (I'm talking > of a couple of weeks ago, when this patch was not part of this series - it > was on its own until Ira Weiny asked me to gather 4 patches in one only > series). Sure. > > This indicates the "migration" is disabled for > > !PREEMPT_RT which is not the case. > > I read again how kmap_atomic() is defined. There are lots of 'if' > statements. Only if the code gets to __kmap_local_pfn_prot(), users can be > assured that it unconditionally calls both migrate_disable() and > preempt_disable(). Right, that part. Then keep it. > > So maybe something like > > > > * Unmaps an address previously mapped by kmap_atomic() and re-enables > > * pagefaults, CPU migration (CONFIG_PREEMPT_RT) or preemption > > * (!CONFIG_PREEMPT_RT). Mappings should be unmapped in the reverse > > > > will make it clear. > > I'm starting to think that this level of detail is too much for users who > just need to understand how to use this function as well as > kmap_local_page(). > > I prefer something like the following: > > + * Unmaps an address previously mapped by kmap_atomic() and re-enables > + * pagefaults and possibly also CPU migration and/or preemption. However, > + * users should not count on disable of migration and/or preemption as a > + * side effect of calling kmap_atomic(). Mappings must be unmapped in the > + * reverse [...] > > I'd also like to write the same paragraph for kmap_local_page(). > > What do you think of being less detailed and instead using the text I wrote > above? Sounds perfect. > Thanks, > > Fabio Sebastian
