Re: [PATCH 1/3] mm/mincore: make mincore() more conservative

[Dominique Martinet <asmadeus@codewreck.org>]

Jiri Kosina wrote on Thu, Mar 07, 2019:
> > I'm not sure this is correct in all cases.   If
> > 
> > 	addr = 4095
> > 	vma->vm_end = 4096
> > 	pages = 1000
> > 
> > then `end' is 4096 and `(end - addr) << PAGE_SHIFT' is zero, but it
> > should have been 1.
> 
> Good catch! It should rather be something like
> 
> 	unsigned long pages = (end >> PAGE_SHIFT) - (addr >> PAGE_SHIFT);

That would be 0 for addr = 0 and vma->vm_end = 1; I assume we would
still want to count that as one page.
I'm not too familiar with this area of the code, but I think there's a
handy macro we can use for this, perhaps
  DIV_ROUND_UP(end - addr, PAGE_SIZE) ?

kernel/kexec_core.c has defined PAGE_COUNT() which seems more
appropriate but I do not see a global equivalent
#define PAGE_COUNT(x) (((x) + PAGE_SIZE - 1) >> PAGE_SHIFT)

-- 
Dominique