On Tue, Jul 23, 2013 at 05:16:07PM +0800, Bob Liu wrote: > On 07/23/2013 03:34 AM, Seth Jennings wrote: > > Right now, zswap can only be enabled at boot time. This patch > > modifies zswap so that it can be dynamically enabled or disabled > > at runtime. > > > > In order to allow this ability, zswap unconditionally registers as a > > frontswap backend regardless of whether or not zswap.enabled=1 is passed > > in the boot parameters or not. This introduces a very small overhead > > for systems that have zswap disabled as calls to frontswap_store() will > > call zswap_frontswap_store(), but there is a fast path to immediately > > return if zswap is disabled. > > There is also overhead in frontswap_load() after all pages are faulted > back into memory. This is true. However frontswap_load() (__frontswap_load() to be more precise) will not call into the backend since the bit in the frontswap_map will not be set. But there is the overhead of checking that bit, you're right. > > > > > Disabling zswap does not unregister zswap from frontswap. It simply > > blocks all future stores. > > > > Signed-off-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx> > > --- > > Documentation/vm/zswap.txt | 18 ++++++++++++++++-- > > mm/zswap.c | 9 +++------ > > 2 files changed, 19 insertions(+), 8 deletions(-) > > > > diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt > > index 7e492d8..d588477 100644 > > --- a/Documentation/vm/zswap.txt > > +++ b/Documentation/vm/zswap.txt > > @@ -26,8 +26,22 @@ Zswap evicts pages from compressed cache on an LRU basis to the backing swap > > device when the compressed pool reaches it size limit. This requirement had > > been identified in prior community discussions. > > > > -To enabled zswap, the "enabled" attribute must be set to 1 at boot time. e.g. > > -zswap.enabled=1 > > +Zswap is disabled by default but can be enabled at boot time by setting > > +the "enabled" attribute to 1 at boot time. e.g. zswap.enabled=1. Zswap > > +can also be enabled and disabled at runtime using the sysfs interface. > > +An exmaple command to enable zswap at runtime, assuming sysfs is mounted > > +at /sys, is: > > + > > +echo 1 > /sys/modules/zswap/parameters/enabled > > + > > +When zswap is disabled at runtime, it will stop storing pages that are > > +being swapped out. However, it will _not_ immediately write out or > > +fault back into memory all of the pages stored in the compressed pool. > > I don't know what's you use case of adding this feature. Dave expressed interest in having it, useful for testing, and I can see people that just wanting to try it out enabling it manually at runtime. > In my opinion I'd perfer to flush all the pages stored in zswap when > disabled it, so that I can run testing without rebooting the machine. Why would you have to reboot your machine? If you want to force all the pages out of the compressed pool, a swapoff should do it as now noted in the Documentation file (below). Seth > > > +The pages stored in zswap will continue to remain in the compressed pool > > +until they are either invalidated or faulted back into memory. In order > > +to force all pages out of the compressed pool, a swapoff on the swap > > +device(s) will fault all swapped out pages, included those in the > > +compressed pool, back into memory. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>