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

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Message-ID: <20170223155827.GB4031@cmpxchg.org>
Date:   Thu, 23 Feb 2017 10:58:27 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Shaohua Li <shli@...com>
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

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.

> @@ -561,20 +567,26 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
>  }
>  
>  
> -static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
> +static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
>  			    void *arg)
>  {
> -	if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
> -		int file = page_is_file_cache(page);
> -		int lru = page_lru_base_type(page);
> +	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
> +	    !PageUnevictable(page)) {
> +		bool active = PageActive(page);
>  
> -		del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE);
> +		del_page_from_lru_list(page, lruvec, LRU_INACTIVE_ANON + active);
>  		ClearPageActive(page);
>  		ClearPageReferenced(page);
> -		add_page_to_lru_list(page, lruvec, lru);
> +		/*
> +		 * lazyfree pages are clean anonymous pages. They have
> +		 * SwapBacked flag cleared to destinguish normal anonymous
> +		 * pages

distinguish

Otherwise, looks great to me. Thanks!