linux-kernel - Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE

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Date:   Thu, 23 Feb 2017 08:26:03 -0800
From:   Shaohua Li <shli@...com>
To:     Johannes Weiner <hannes@...xchg.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <Kernel-team@...com>, <mhocko@...e.com>, <minchan@...nel.org>,
        <hughd@...gle.com>, <riel@...hat.com>,
        <mgorman@...hsingularity.net>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE
 list

On Thu, Feb 23, 2017 at 10:58:27AM -0500, Johannes Weiner wrote:
> Hi Shaohua,
> 
> On Wed, Feb 22, 2017 at 10:50:41AM -0800, Shaohua Li wrote:
> > @@ -268,6 +268,12 @@ static void __activate_page(struct page *page, struct lruvec *lruvec,
> >  		int lru = page_lru_base_type(page);
> >  
> >  		del_page_from_lru_list(page, lruvec, lru);
> > +		if (PageAnon(page) && !PageSwapBacked(page)) {
> > +			SetPageSwapBacked(page);
> > +			/* charge to anon scanned/rotated reclaim_stat */
> > +			file = 0;
> > +			lru = LRU_INACTIVE_ANON;
> > +		}
> 
> As per my previous feedback, please remove this. Write-after-free will
> be caught and handled in the reclaimer, read-after-free is a bug that
> really doesn't require optimizing page aging for. And we definitely
> shouldn't declare invalid data suddenly valid because it's being read.

GUP could run into this. Don't we move the page because it's hot? I think it's
not just about page aging. If we leave the page there, page reclaim will just
waste time to reclaim the pages which should't be reclaimed.

Thanks,
Shaohua