Re: [PATCH 5/7] vfs: Add wbcflush sysfs knob to disable storagedevice writeback cache flushes

[Jeff Garzik]

Bartlomiej Zolnierkiewicz wrote:
> calling fsync() after every mail fetched.  Adding mandatory cache flush
> to it only makes things worse (again looking from performance POV).
>
> BTW in Linux world we never made any guarantees for fsync() on devices
> using write caching:

Quite true, but I've always thought that was trading away correctness 
for performance...  at a critical juncture where a consistency 
checkpoint was explicitly requested by the app.

My ideal would probably be blkdev cache flushing by default on fsync(2), 
with a block layer "desktop mode" knob to turn it off if you don't want it.

The current alternatives -- mount sync or disable blkdev writeback cache 
-- are far, far slower and punish the entire system just to provide a 
consistency checkpoint for a handful of fsync-needful apps.

	Jeff


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