[Linux-cachefs] Re: Finding fscache contents for a file

["John Groves" <John groves net>]

I'd like to add one more question... when I explicitly clean out the page
cache, so as to force reads to be satisfied from the fscache, I frequently
find that not all of my pages are available from the fscache.  I don't know
why this is, but I suspect that calling my releasepage method (from an
ioctl, after loading the cache & fscache) sometimes frees the page(s) before
fscache gets around to storing them...though that doesn't make sense if
fscache bumps the page reference count until it has made a copy or written
it out.  (does fscache consider my page dirty for the purpose of writing to
cachefiles, or does it make a copy, and is it susceptible to having a page
freed out from under it?...in which case is there a way to perform an
explicit flush [preferably on the whole file/object rather than one page at
a time]?

I would appreciate suggestions as to how to sort this out.

Thanks,
John Groves

On Mon, Nov 10, 2008 at 6:03 PM, John Groves <John groves net> wrote:

> I have modified the lustre client filesystem to use fscache, and it is in a
> rudimentary working state.  Among my most pressing requirements is to purge
> the fscache for any extent for which a DLM lock is revoked.
>
> To the end of proving that functionality, I would like to give myself a
> file ioctl that would determine what is in the fscache for a given file.
> Since this is for testing, performance isn't a major concern.  I'm already
> doing this with the page cache, and I hope something similar would be
> possible with the fscache.
>
> Is there a supported way to query whether a given page_index is in the
> fscache?  If not, I'd appreciate suggestions as to how to go about this (or
> insight into how other implementers have proven functionality without this
> feature).  I'm fairly ignorant as to the internals of fscache...
>
> Thanks,
> John Groves
>