linux-kernel - Re: [PATCH v2 01/13] mm: support madvise(MADV

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Date:	Thu, 5 Nov 2015 12:41:20 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-api@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jason Evans <je@...com>, Daniel Micay <danielmicay@...il.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Shaohua Li <shli@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	yalin.wang2010@...il.com
Subject: Re: [PATCH v2 01/13] mm: support madvise(MADV_FREE)

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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