speed up dirty data cleaning

speed up dirty data cleaning

[Stefan Priebe - Profihost AG]

Hi,

today i had the problem that my caching device was nearly full and
bcache seemed tom react very slowly. Strangely i did not see continues
writes to the disk to clean the cache.

Is there any way to speed up dirty data cleaning.

Stefan

Re: speed up dirty data cleaning

[Stefan Priebe - Profihost AG]

After some time it seems to start writing out all the data at a good
disk speed.

But how does bcache determine when to write which kind of data out of
bcache.

Stefan

Am 07.11.2013 14:09, schrieb Stefan Priebe - Profihost AG:
> Hi,
> 
> today i had the problem that my caching device was nearly full and
> bcache seemed tom react very slowly. Strangely i did not see continues
> writes to the disk to clean the cache.
> 
> Is there any way to speed up dirty data cleaning.
> 
> Stefan
> 

Re: speed up dirty data cleaning

[Kent Overstreet]

On Thu, Nov 07, 2013 at 04:18:35PM +0100, Stefan Priebe - Profihost AG wrote:
> After some time it seems to start writing out all the data at a good
> disk speed.
> 
> But how does bcache determine when to write which kind of data out of
> bcache.

There's a PD controller that tries to keep the amount of dirty data at
writeback_percent percentage of your cache size. But, since the dirty data
account was _still_ broken, that would screw up that PD controller.

Workaround is to set writeback_percent to 0

Re: speed up dirty data cleaning

[Stefan Priebe - Profihost AG]

Am 08.11.2013 03:49, schrieb Kent Overstreet:
> On Thu, Nov 07, 2013 at 04:18:35PM +0100, Stefan Priebe - Profihost AG wrote:
>> After some time it seems to start writing out all the data at a good
>> disk speed.
>>
>> But how does bcache determine when to write which kind of data out of
>> bcache.
> 
> There's a PD controller that tries to keep the amount of dirty data at
> writeback_percent percentage of your cache size. But, since the dirty data
> account was _still_ broken, that would screw up that PD controller.
> 
> Workaround is to set writeback_percent to 0

Tried that but it doesn't seem to start cleaning correctly.

Stefan