Re: Possible Idea with filesystem buffering.

Hans Reiser
2002-01-20T21:35:01Z

Rik van Riel wrote:

>On Mon, 21 Jan 2002, Hans Reiser wrote:
>
>>Rik van Riel wrote:
>>
>>>On Sun, 20 Jan 2002, Hans Reiser wrote:
>>>
>
>>>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,
>>
>
>That is exactly what the VM does.
>
So basically you continue to believe that one cache manager shall rule
them all, and in the darkness as to their needs, bind them.

>
>
>>and should otherwise check to see if the filesystem supports something
>>like pressure_fs_cache(), yes?
>>
>
>That's incompatible with the concept of memory zones.
>
Care to explain more?

>
>
>regards,
>
>Rik
>