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

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Message-ID: <Pine.LNX.4.64.0701041653250.12920@blonde.wat.veritas.com>
Date:	Thu, 4 Jan 2007 17:09:45 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Bill Davidsen <davidsen@....com>
cc:	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: open(O_DIRECT) on a tmpfs?

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.

Hugh
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