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From: Shakeel Butt <shakeelb@google.com>
Date: Tue, 22 Aug 2017 17:25:00 -0700
Message-ID: <CALvZod73huYukNBUvn3XS40V4SQYk4H5_Jhv4Qp0446-d4P0rg@mail.gmail.com>
Subject: Re: [RFC PATCH] mm: fadvise: avoid fadvise for fs without backing device
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Sender: owner-linux-mm@kvack.org
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To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>, Hillf Danton <hillf.zj@alibaba-inc.com>, Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>, Greg Thelen <gthelen@google.com>, Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>

>> It doesn't sound like a risky change to me, although perhaps someone is
>> depending on the current behaviour for obscure reasons, who knows.
>>
>> What are the reasons for this change?  Is the current behaviour causing
>> some sort of problem for someone?
>
> Yes, one of our generic library does fadvise(FADV_DONTNEED). Recently
> we observed high latency in fadvise() and notice that the users have
> started using tmpfs files and the latency was due to expensive remote
> LRU cache draining. For normal tmpfs files (have data written on
> them), fadvise(FADV_DONTNEED) will always trigger the un-needed remote
> cache draining.
>

Hi Andrew, do you have more comments or concerns?

>>
>>

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