From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bob Liu <bob.liu@oracle.com>
Subject: Re: [patch 9/9] mm: keep page cache radix tree nodes in check
Date: Wed, 15 Jan 2014 13:55:01 +0800
Message-ID: <52D622B5.6070203@oracle.com>
References: <1389377443-11755-1-git-send-email-hannes@cmpxchg.org> <1389377443-11755-10-git-send-email-hannes@cmpxchg.org>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Dave Chinner <david@fromorbit.com>, Greg Thelen <gthelen@google.com>,
        Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Luigi Semenzato <semenzato@google.com>, Mel Gorman <mgorman@suse.de>,
        Metin Doslu <metin@citusdata.com>,
        Michel Lespinasse <walken@google.com>,
        Minchan Kim <minchan.kim@gmail.com>,
        Ozgun Erdogan <ozgun@citusdata.com>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        Roman Gushchin <klamm@yandex-team.ru>, Ryan Mallon <rmallon@gmail.com>,
        Tejun Heo <tj@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
        linux-mm@kvack.org,
To: Johannes Weiner <hannes@cmpxchg.org>
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Hi Johannes,

On 01/11/2014 02:10 AM, Johannes Weiner wrote:
> Previously, page cache radix tree nodes were freed after reclaim
> emptied out their page pointers.  But now reclaim stores shadow
> entries in their place, which are only reclaimed when the inodes
> themselves are reclaimed.  This is problematic for bigger files that
> are still in use after they have a significant amount of their cache
> reclaimed, without any of those pages actually refaulting.  The shadow
> entries will just sit there and waste memory.  In the worst case, the
> shadow entries will accumulate until the machine runs out of memory.
> 

I have one more question. It seems that other algorithm only remember
history information of a limit number of evicted pages where the number
is usually the same as the total cache or memory size.
But in your patch, I didn't see a preferred value that how many evicted
pages' history information should be recorded. It all depends on the
workingset_shadow_shrinker?

Thanks,
-Bob

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