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Date: Tue, 11 Mar 2014 14:27:29 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: implement POSIX_FADV_NOREUSE
Message-Id: <20140311142729.1e3e4e51186db4c8ee49a9f4@linux-foundation.org>
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To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.cz>, Matthias Wirth <matthias.wirth@gmail.com>, Lukas Senger <lukas@fridolin.com>, Matthew Wilcox <matthew@wil.cx>, Jeff Layton <jlayton@redhat.com>, "J. Bruce Fields" <bfields@fieldses.org>, Johannes Weiner <hannes@cmpxchg.org>, Rik van Riel <riel@redhat.com>, Lisa Du <cldu@marvell.com>, Paul Mackerras <paulus@samba.org>, Sasha Levin <sasha.levin@oracle.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Fengguang Wu <fengguang.wu@intel.com>, Shaohua Li <shli@kernel.org>, Alexey Kardashevskiy <aik@ozlabs.ru>, Minchan Kim <minchan@kernel.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Al Viro <viro@zeniv.linux.org.uk>, Steven Whitehouse <swhiteho@redhat.com>, Mel Gorman <mgorman@suse.de>, Cody P Schafer <cody@linux.vnet.ibm.com>, Jiang Liu <liuj97@gmail.com>, David Rientjes <rientjes@google.com>, "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>, Zhang Yanfei <zhangyanfei@cn.fujitsu.com>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, Lukas Czerner <lczerner@redhat.com>, Damien Ramonda <damien.ramonda@intel.com>, Mark Rutland <mark.rutland@arm.com>, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On Tue, 11 Mar 2014 08:24:42 -0700 Dave Hansen <dave.hansen@linux.intel.com> wrote:

> On 03/11/2014 07:06 AM, Michal Hocko wrote:
> >> > In our implementation pages marked with the NoReuse flag are added to
> >> > the tail of the LRU list the first time they are read. Therefore they
> >> > are the first to be reclaimed.
> > page flags are really scarce and I am not sure this is the best usage of
> > the few remaining slots.
> 
> Yeah, especially since the use so so transient.

Yes, we're short on page flags.

> This also looks to ignore the reuse flag for existing pages. 

And it sets PG_noreuse on new pages whether or not they were within the
fadvise range (offset...offset+len).  It's not really an fadvise
operation at all.

A practical implementation might go through the indicated pages, clear
any referenced bits and move them to the tail of the inactive LRU?

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