linux-kernel - Re: [PATCH V3 2/7] mm: move MADV_FREE pages into LRU_INACTIVE

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Date:   Thu, 16 Feb 2017 16:35:25 -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 V3 2/7] mm: move MADV_FREE pages into LRU_INACTIVE_FILE
 list

On Thu, Feb 16, 2017 at 12:52:53PM -0500, Johannes Weiner wrote:
> On Tue, Feb 14, 2017 at 11:36:08AM -0800, Shaohua Li wrote:
> > @@ -126,4 +126,24 @@ static __always_inline enum lru_list page_lru(struct page *page)
> >  
> >  #define lru_to_page(head) (list_entry((head)->prev, struct page, lru))
> >  
> > +/*
> > + * lazyfree pages are clean anonymous pages. They have SwapBacked flag cleared
> > + * to destinguish normal anonymous pages.
> > + */
> > +static inline void set_page_lazyfree(struct page *page)
> > +{
> > +	VM_BUG_ON_PAGE(!PageAnon(page) || !PageSwapBacked(page), page);
> > +	ClearPageSwapBacked(page);
> > +}
> > +
> > +static inline void clear_page_lazyfree(struct page *page)
> > +{
> > +	VM_BUG_ON_PAGE(!PageAnon(page) || PageSwapBacked(page), page);
> > +	SetPageSwapBacked(page);
> > +}
> > +
> > +static inline bool page_is_lazyfree(struct page *page)
> > +{
> > +	return PageAnon(page) && !PageSwapBacked(page);
> > +}
> 
> Sorry for not getting to v2 in time, but I have to say I strongly
> agree with your first iterations and would much prefer this to be
> open-coded.
> 
> IMO this needlessly introduces a new state opaquely called "lazyfree",
> when really that's just anonymous pages that don't need to be swapped
> before reclaim - PageAnon && !PageSwapBacked. Very simple MM concept.
> 
> That especially shows when we later combine it with page_is_file_cache
> checks like the next patch does.
> 
> The rest of the patch looks good to me.

Thanks! I do agree checking PageSwapBacked is clearer, but Minchan convinced me
because of the accounting issue. Where do you suggest we should put the
accounting to?

Thanks,
Shaohua