Re: o_sync in vfat driver

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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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