Re: [PATCH v2 2/2] mm/memory_hotplug: fix hwpoisoned large folio handling in do_migrate_range

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

> > > > So we will need to take care of madvise cold or pageout case?
> > > > 
> > > > Hi Matthew, Pankaj, and Luis,
> > > > 
> > > > Is it possible to partially map a min-order folio in a fs with LBS? Based on my
> > > 
> > > Typically, FSs match the min order with the blocksize of the filesystem.
> > > As a filesystem block is the smallest unit of data that the filesystem uses
> > > to store file data on the disk, we cannot partially map them.
> > > 
> > > So if I understand your question correctly, the answer is no.
> 
> I'm confused. Shouldn't this be trivially possible?
> 
Hmm, maybe I misunderstood the question?

> E.g., just mmap() a single page of such a file? Who would make that fail?
> 

My point was, even if you try to mmap a single page of a file, page
cache will read the whole block (that corresponds to min order folio).

Technically we can mmap a single page of file, but FS will always read
and write **at least** in min folio order chunks.

> And if it doesn't fail, who would stop us from munmap()'ing everything
> except a single page.
> 
> -- 
> Cheers,
> 
> David / dhildenb
> 
> 

--
Pankaj