[PATCH 1/3] Add r/w sysfs attribute for zcache_freeze

Florian Schmaus fschmaus at gmail.com
Thu Mar 15 17:43:01 UTC 2012

On 03/15/12 17:37, Konrad Rzeszutek Wilk wrote:
> On Tue, Mar 13, 2012 at 11:34:46AM +0100, Florian Schmaus wrote:
>> From: Andor Daam<andor.daam at googlemail.com>
>> This patch makes dynamic enabling/disabling of zcache via a sysfsnode possible.
> There should be an patch to the Documentation/ABI/testing for these parameters.
Agreed. Currently none of the modifiable zcache parameters has any 
Documentation in ABI/testing, including:
- zv_max_zsize
- zv_max_mean_zsize
- zv_page_count_policy

We are also thinking about providing a patch that moves all read only 
zcache sysfs attributes into debugfs, so that the debug values from 
cleancache, frontswap and zcache are all within /sys/kernel/debug. It 
has also the advantage that if one doesn't want the performance impact 
of those counters, he could easily compile zcache without them.
This patch could also include the missing Documentation.
>> The node is used to toggle the preexisting zcache_freeze variable to
>> stop/start accepting pages by zcache.
> What is the reasoning to do this in the frontend instead of the backend (Cleancache/frontswap)?
Not sure if you just confused frontend with backend. We always thought like
frontend: cleancache/frontswap
backend: zcache (or Xen tmem, ...)

The reason to disable ("freeze") zcache via an mm/zcache sysfs interface 
is simply that this only affects zcache behavior and not the frontend(s) 
nor any other registered backend (which isn't currently possible anyways).


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