Re: [RFC] pass FAF flag to perfuse

[Chuck Silvers <chuq%chuq.com@localhost>]

On Tue, Jun 05, 2012 at 01:01:25PM +0000, Emmanuel Dreyfus wrote:
> Hi
> 
> PUFFS sometimes uses Fire-And-Forget (FAF) operation, where the
> request is sent to userland but the result is not awaited. This
> always happens for close, inactive and reclaim, and optionnaly
> happens for fsync, setattr (during fsync), and write (during putpages).
> 
> There is a ressource leak when the filesystem is getting unresponsive
> and the kernel keeps sending requests. perfuse and puffs hold buffer 
> in userspace related to the requests, and this may last for a while.
> 
> Attached patch makes sure a puffs filesystem can be informed that 
> a fsync, setattr or write is in FAF mode. libperfuse use it to avoid
> awaiting for the reply of theses operations. Of course, we still
> get FUSE replies, but we ignore them except if there is an error. In
> that later case, we abort.
> 
> Opinions?

if this new flag is for userland only, why would you need to
assign an IO_* flag for it in the kernel?  it would be better to keep
this out of the kernel's flags if it doesn't need to be there.

-Chuck


> Index: sys/sys/vnode.h
> ===================================================================
> RCS file: /cvsroot/src/sys/sys/vnode.h,v
> retrieving revision 1.236
> diff -U4 -r1.236 vnode.h
> --- sys/sys/vnode.h   24 Nov 2011 15:51:30 -0000      1.236
> +++ sys/sys/vnode.h   5 Jun 2012 12:35:23 -0000
> @@ -289,8 +289,9 @@
>  #define      IO_NORMAL       0x00800         /* operate on regular data */
>  #define      IO_EXT          0x01000         /* operate on extended 
> attributes */
>  #define      IO_DIRECT       0x02000         /* direct I/O hint */
>  #define      IO_JOURNALLOCKED 0x04000        /* journal is already locked */
> +#define      IO_FAF          0x08000         /* FAF bit for PUFFS (userland 
> only) */
>  #define      IO_ADV_MASK     0x00003         /* access pattern hint */
>  
>  #define      IO_ADV_SHIFT    0
>  #define      IO_ADV_ENCODE(adv)      (((adv) << IO_ADV_SHIFT) & IO_ADV_MASK)