linux-kernel - Re: [PATCH RFC 3/4] mm: move lazy free pages to inactive list

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Message-ID: <20150225151746.GG26680@dhcp22.suse.cz>
Date:	Wed, 25 Feb 2015 16:17:46 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>, Shaohua Li <shli@...nel.org>,
	Yalin.Wang@...ymobile.com
Subject: Re: [PATCH RFC 3/4] mm: move lazy free pages to inactive list

On Wed 25-02-15 09:27:28, Minchan Kim wrote:
> On Tue, Feb 24, 2015 at 05:14:08PM +0100, Michal Hocko wrote:
> > On Tue 24-02-15 17:18:16, Minchan Kim wrote:
> > > MADV_FREE is hint that it's okay to discard pages if memory is
> > > pressure and we uses reclaimers(ie, kswapd and direct reclaim)
> > 
> > s@if memory is pressure@if there is memory pressure@
> > 
> > > to free them so there is no worth to remain them in active
> > > anonymous LRU list so this patch moves them to inactive LRU list.
> > 
> > Makes sense to me.
> > 
> > > A arguable issue for the approach is whether we should put it
> > > head or tail in inactive list
> > 
> > Is it really arguable? Why should active MADV_FREE pages appear before
> > those which were living on the inactive list. This doesn't make any
> > sense to me.
> 
> It would be better to drop garbage pages(ie, freed from allocator)
> rather than swap out and now anon LRU aging is seq model so
> inacitve list can include a lot working set so putting hinted pages
> into tail of LRU could enhance reclaim efficiency.
> That's why I said it might be arguble.

OK, maybe I misunderstood what you tried to tell. Sure we can discuss
whether to put all MADV_FREE pages to the tail of inactive list. But
the above wording suggested that _active_ MADV_FREE pages were
discussed and treating them differently from the inactive pages simply
didn't make sense to me.
 
[...]
-- 
Michal Hocko
SUSE Labs
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