Messages in this thread | | | Date | Mon, 30 Mar 2009 15:09:25 -0400 | From | Jeff Garzik <> | Subject | Re: [PATCH 5/7] vfs: Add wbcflush sysfs knob to disable storage device writeback cache flushes |
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Jens Axboe wrote: > On Mon, Mar 30 2009, Jeff Garzik wrote: >> Jens Axboe wrote: >>> On Mon, Mar 30 2009, Bartlomiej Zolnierkiewicz wrote: >>>> On Monday 30 March 2009, Fernando Luis Vázquez Cao wrote: >>>>> Add a sysfs knob to disable storage device writeback cache flushes. >>>> The horde of casual desktop users (with me included) would probably prefer >>>> having two settings -- one for filesystem barriers and one for fsync(). >>>> >>>> IOW I prefer higher performance at the cost of risking losing few last >>>> seconds/minutes of work in case of crash / powerfailure but I would still >>>> like to have the filesystem in the consistent state after such accident. >>> The knob is meant to control whether we really need to send a flush to >>> the device or not, so it's an orthogonal issue to what you are talking >>> about. For battery backed caches, we never need to flush. This knob is >>> useful IFF we have devices with write back caches that STILL do a cache >>> flush. >> How do installers and/or kernels detect a battery-backed cache that does >> not need flush? > > They obviously can't, otherwise it would not be an issue at all. And > whether it's an issue is up for debate, until someone can point at such > a device. You could add a white/blacklist.
Sorry, I guess I misinterpreted your dual "IFF" statement :)
I completely agree that the suggested knob, for disabling cache flush for these battery-backed devices, is at the present time addressing an entirely theoretical argument AFAICS.
Jeff
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