Re: [fuse-devel] direct_io versus mmap()

[sage w. <sa...@ne...>]

On Thu, 28 Jul 2005, Miklos Szeredi wrote:
> FUSE always does write-through.  No dirty buffers ever accumulate.

Ok, that avoids half the problem...

>> Also, now that I think about it, I remember somebody mentioning that you
>> can somehow enable/disable direct_io on a per-file basis... is that true?
>
> That is the plan.  Next release will have this.

Okay.  Although in order for this to fully solve my problem there's need 
to be a way to tell if a given file is being mmap()'d, and to selectively 
disable it.  Doesn't sound very elegant..

> I think you should.  Do you know when the cache needs to be
> invalidated?  Currenty you can do that by opening and closing the file
> you want the cache to be purged for.

Are you suggesting that the FUSE user process open and close the file to 
kick the kernel?  And that would really flush pages even though another 
process has hte file open the whole time?

It's not so much that I need to periodically purge all pages, it's that I 
need to force all reads to be synchronous for some indefinite period. 
When processes on different nodes have a file open for both reading and 
writing, all reads and writes have to go to the server to get correct 
behavior.  I supposed after every read operation completes I could kick 
the kernel into purging pages...?

sage