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Date: Wed, 09 Oct 2002 12:55:32 +0200 (CEST)
From: Giuliano Pochini <pochini@shiny.it>
To: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] O_STREAMING - flag for optimal streaming I/O
Cc: Andrew Morton <akpm@digeo.com>
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On 09-Oct-2002 Andrew Morton wrote:
> Giuliano Pochini wrote:
>> 
>> > The point of O_STREAMING is one change: drop pages in the pagecache
>> > behind our current position, that are free-able, because we know we will
>> > never want them.
>>
>> Does it drop pages unconditionally ?
>
> Yup.
>
>> What happens if I do a
>> streaming_cat largedatabase > /dev/null while other processes
>> are working on it ?
>
> You'll make your database run really slowly.
>
>> It's not a good thing to remove the whole
>> cached data other apps are working on.
>
> Don't do that then ;)

I was thinking about hot backups of databases. But even if it
did not drop caches "shared" by other processes it would drop
them anyway because write-behind is still on. Probably only
O_DIRECT can help in this case.

> Seriously, there are tons of ways of creating local performance
> DoS'es of this form.  fsync is an excellent tool for that.

Yes, I'm aware of that.


Bye.

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