Re: o_sync in vfat driver

[Mathis Ahrens <Mathis.Ahrens@gmx.de>]

Hi all,

Chris Mason wrote:
> On Monday 27 February 2006 18:12, Andrew Morton wrote:
>   
> > We don't know that the same number of same-sized write()s were happening in
> > each case.
> >
> > There's been some talk about implementing fsync()-on-file-close for this
> > problem, and some protopatches.  But nothing final yet.
> >     
>
> Here's the patch I'm using in -suse right now.  What I want to do is make a 
> much more generic -o flush, but it'll still need a few bits in individual 
> filesystem to kick off metadata writes quickly.
>
> The basic goal behind the code is to trigger writes without waiting for both
> data and metadata.  If the user is watching the memory stick, when the 
> little light stops flashing all the data and metadata will be on disk.
>
> It also generally throttles userland a little during file release.  This 
> could be changed to throttle for each page dirtied, but most users I 
> asked liked the current setup better.
>   

I like the idea and would like to see something like this in mainline.

Here is some non-scientific benchmark done with 2.6.16, comparing
default mount and flush mount of a USB2 stick:

/////////////////////////////////////////////////////////////////////
Single File "Test": 43MB
$ time cp Test /media/usbdisk/test/ && time umount /media/usbdisk/
/////////////////////////////////////////////////////////////////////

VANILLA:

real    0m3.770s
user    0m0.004s
sys     0m0.308s

real    0m9.439s
user    0m0.000s
sys     0m0.040s

FLUSH:

real    0m6.000s
user    0m0.012s
sys     0m0.400s

real    0m3.668s
user    0m0.000s
sys     0m0.028s

REAL TIME RATIO (FLUSH/VANILLA):
9.6 / 13.1 = 0.73

/////////////////////////////////////////////////////////////////////
Directory Tree "flushtest": 44MB (8866 files, 1820 dirs)
$ time cp -R flushtest/ /media/usbdisk/ && time umount /media/usbdisk/
/////////////////////////////////////////////////////////////////////

VANILLA:

real    0m0.966s
user    0m0.024s
sys     0m0.860s

real    1m11.962s
user    0m0.004s
sys     0m0.160s

FLUSH:

real    1m41.645s
user    0m0.032s
sys     0m1.112s

real    0m4.660s
user    0m0.004s
sys     0m0.068s

REAL TIME RATIO (FLUSH/VANILLA):
106.3 / 77.9 = 1.36

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