Re: [RFC PATCH 3/10] define page_file_cache

Christoph Lameter
2007-11-07T02:23:44Z

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.