Re: [RFC PATCH 3/10] define page_file_cache
From: Christoph Lameter
Date: Tue Nov 06 2007 - 21:23:54 EST
On Sat, 3 Nov 2007, Rik van Riel wrote:
> Define page_file_cache() function to answer the question:
> is page backed by a file?
Well its not clear what is meant by a file in the first place.
By file you mean disk space in contrast to ram based filesystems?
I think we could add a flag to the bdi to indicate wheter the backing
store is a disk file. In fact you can also deduce if if a device has
no writeback capability set in the BDI.
> Unfortunately this needs to use a page flag, since the
> PG_swapbacked state needs to be preserved all the way
> to the point where the page is last removed from the
> LRU. Trying to derive the status from other info in
> the page resulted in wrong VM statistics in earlier
> split VM patchsets.
The bdi may avoid that extra flag.
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