Re: [PATCH v2 01/13] mm: support madvise(MADV_FREE)

[Sergey Senozhatsky]

Hi Minchan,

On (11/05/15 08:39), Minchan Kim wrote:
[..]
> > 
> > I think it makes sense to update pmd_trans_unstable() and
> > pmd_none_or_trans_huge_or_clear_bad() comments in asm-generic/pgtable.h
> > Because they explicitly mention MADV_DONTNEED only. Just a thought.
> 
> Hmm, When I read comments(but actually I don't understand it 100%), it
> says pmd disappearing from MADV_DONTNEED with mmap_sem read-side
> lock. But MADV_FREE doesn't remove the pmd. So, I don't understand
> what I should add comment. Please suggest if I am missing something.
> 

Hm, sorry, I need to think about it more, probably my comment is irrelevant.
Was fantasizing some stupid use cases like doing MADV_DONTNEED and MADV_FREE
on overlapping addresses from different threads, processes that share mem, etc.

> > > @@ -379,6 +502,14 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
> > >  		return madvise_remove(vma, prev, start, end);
> > >  	case MADV_WILLNEED:
> > >  		return madvise_willneed(vma, prev, start, end);
> > > +	case MADV_FREE:
> > > +		/*
> > > +		 * XXX: In this implementation, MADV_FREE works like
> > 		  ^^^^
> > 		XXX
> 
> What does it mean?

not much. just a minor note that there is a 'XXX' in "XXX: In this implementation"
comment.

	-ss
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