Messages in this thread | | | Date | Thu, 24 Sep 2009 12:50:00 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH RFC 1/2] Add notifiers for various swap events |
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On Thu, 24 Sep 2009 08:40:56 +0530 Nitin Gupta <ngupta@vflare.org> wrote:
> On 09/24/2009 07:17 AM, KAMEZAWA Hiroyuki wrote: > > On Mon, 21 Sep 2009 19:03:59 +0530 > > Nitin Gupta <ngupta@vflare.org> wrote: > > > >> Add notifiers for following swap events: > >> - Swapon > >> - Swapoff > >> - When a swap slot is freed > >> > >> This is required for ramzswap module which implements RAM based block > >> devices to be used as swap disks. These devices require a notification > >> on these events to function properly (as shown in patch 2/2). > >> > >> Currently, I'm not sure if any of these event notifiers have any other > >> users. However, adding ramzswap specific hooks instead of this generic > >> approach resulted in a bad/hacky code. > >> > > Hmm ? if it's not necessary to make ramzswap as module, for-ramzswap-only > > code is much easier to read.. > > > > The patches posted earlier (v3 patches) inserts special hooks for swap slot > free event only. In this version, the callback is set when we get first R/W request. > Actually ramzswap needs callback for swapon/swapoff too but I just didn't do it. > > Then Pekka posted test patch that allows setting this callback during swapon > itself. Looking that all these patches, I realized its already too messy even > if we just make everything ramzswap specific. > Just FYI, Pekka's test patch: > http://patchwork.kernel.org/patch/48472/ > > Then I added this generic notifier interface which, compared to earlier version, > looks much cleaner. The code to add these notifiers is also very small. > ya, yes. the patch itsels seems clean.
> > > > > >> For SWAP_EVENT_SLOT_FREE, callbacks are made under swap_lock. Currently, this > >> is not a problem since ramzswap is the only user and the callback it registers > >> can be safely made under this lock. However, if this event finds more users, > >> we might have to work on reducing contention on this lock. > >> > >> Signed-off-by: Nitin Gupta <ngupta@vflare.org> > >> > > > > In general, notifier chain codes allowed to return NOTIFY_BAD. > > But this patch just assumes all chains should return NOTIFY_OK or > > just ignore return code. > > > > That's not good as generic interface, I think. > > > What action we can take here if the notifier_call_chain() returns an error (apart > from maybe printing an error)? Perhaps we can add a warning in case of swapon/off > events but not in case of swap slot free event which is called under swap_lock. > If return code is ignored, please add commentary at least.
I wonder I may able to move memcg's swap_cgroup code for swapon/swapoff onto this notifier. (swap_cgroup_swapon/swap_cgroup_swapoff) But it seems not. sorry for bothering you.
Thanks, -Kame
> > > Thanks, > Nitin >
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