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Date: Mon, 21 Jan 2002 00:15:28 +0300
From: Hans Reiser <reiser@namesys.com>
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To: Rik van Riel <riel@conectiva.com.br>
CC: Shawn <spstarr@sh0n.net>, linux-kernel@vger.kernel.org,
        Josh MacDonald <jmacd@CS.Berkeley.EDU>
Subject: Re: Possible Idea with filesystem buffering.
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Rik van Riel wrote:

>On Sun, 20 Jan 2002, Hans Reiser wrote:
>
>>Write clustering is one thing it achieves.
>>
>>Flushing everything involved in a transaction ... is another thing.
>>
>
>Agreed on these points, but you really HAVE TO work towards
>flushing the page ->writepage() gets called for.
>
>Think about your typical PC, with memory in ZONE_DMA,
>ZONE_NORMAL and ZONE_HIGHMEM. If we are short on DMA pages
>we will end up calling ->writepage() on a DMA page.
>
>If the filesystem ends up writing completely unrelated pages
>and marking the DMA page in question referenced the VM will
>go in a loop until the filesystem finally gets around to
>making a page in the (small) DMA zone freeable ...
>

This is a bug in VM design, yes?  It should signal that it needs the 
particular page written, which probnably means that it should use 
writepage only when it needs that particular page written, and should 
otherwise check to see if the filesystem supports something like 
pressure_fs_cache(), yes?

>
>
>regards,
>
>Rik
>



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