linux-kernel - Re: open(O_DIRECT) on a tmpfs?

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Message-ID: <459D3F4A.5070904@redhat.com>
Date:	Thu, 04 Jan 2007 12:54:18 -0500
From:	Peter Staubach <staubach@...hat.com>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Bill Davidsen <davidsen@....com>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: open(O_DIRECT) on a tmpfs?

Hugh Dickins wrote:
> On Thu, 4 Jan 2007, Bill Davidsen wrote:
>   
>> In many cases the use of O_DIRECT is purely to avoid impact on cache used by
>> other applications. An application which writes a large quantity of data will
>> have less impact on other applications by using O_DIRECT, assuming that the
>> data will not be read from cache due to application pattern or the data being
>> much larger than physical memory.
>>     
>
> I see that as a good argument _not_ to allow O_DIRECT on tmpfs,
> which inevitably impacts cache, even if O_DIRECT were requested.
>
> But I'd also expect any app requesting O_DIRECT in that way, as a caring
> citizen, to fall back to going without O_DIRECT when it's not supported.

I suppose that one could also argue that the backing store for tmpfs
is the memory itself and thus, O_DIRECT could or should be supported.

    Thanx...

       ps
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