Re: Off-Topic Write cache disabling?

[Bernd Schubert <bernd.schubert@fastmail.fm>]

On 02/03/2015 06:45 PM, Weedy wrote:
> Is there a kernel option or sysfs toggle that disables write caching?
> Or forces the kernel to commit everything constantly.
> 
> ------
> I don't really want to join another ML, especially a higher traffic
> one just to ask this when it only bugs me sometimes. But I'll shut up
> if this is unwanted.
> ------
> 
> I use a similar kernel config with respect to selected options on all
> my systems but this only effect my laptop.
> On any of my personal system or system I have remote access too
> nr_dirty drifts up and down and nr_writeback stays around 0 (assuming
> the system isn't working hard).
> On my laptop both nr_dirty and nr_writeback stay at 0. I can make them
> go up to 10ish if I untar something but then almost immediately go
> back to 0. If I didn't know better I would swear dirty_*_centisecs or
> something was set to a near instant commit interval but I haven't
> found evidence of that. The hard drive light blinks almost constantly
> once a second, even if I'm at a X login screen.
> As I said this doesn't bug me most of the time but if I let my FF
> session get too large or start multiple VMs anything that might make
> me swap a little, the machine pretty much dies from IOWAIT. Which I'm
> guessing is because it's trying to flush (syncfs?) imediately and
> constantly.
> 
> You guys spend all day in the IO subsystem, any idea where I can keep
> looking? It has persisted across reboots and kernel updates.


Try mount -osync or force your application to write with direct IO.


Cheers,
Bernd