Messages in this thread |  | | Date | Thu, 12 Jul 2012 10:15:55 +0900 | | From | Minchan Kim <> | | Subject | Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate |
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On Wed, Jul 11, 2012 at 09:15:43AM -0500, Seth Jennings wrote: > On 07/11/2012 02:42 AM, Minchan Kim wrote: > > On 07/11/2012 12:17 AM, Seth Jennings wrote: > >> On 07/09/2012 09:35 PM, Minchan Kim wrote: > >>> Maybe we need local_irq_save/restore in zs_[un]map_object path. > >> > >> I'd rather not disable interrupts since that will create > >> unnecessary interrupt latency for all users, even if they > > > > Agreed. > > Although we guide k[un]map atomic is so fast, it isn't necessary > > to force irq_[enable|disable]. Okay. > > > >> don't need interrupt protection. If a particular user uses > >> zs_map_object() in an interrupt path, it will be up to that > >> user to disable interrupts to ensure safety. > > > > Nope. It shouldn't do that. > > Any user in interrupt context can't assume that there isn't any other user using per-cpu buffer > > right before interrupt happens. > > > > The concern is that if such bug happens, it's very hard to find a bug. > > So, how about adding this? > > > > void zs_map_object(...) > > { > > BUG_ON(in_interrupt()); > > } > > I not completely following you, but I think I'm following > enough. Your point is that the per-cpu buffers are shared > by all zsmalloc users and one user doesn't know if another > user is doing a zs_map_object() in an interrupt path.
And vise versa is yes.
> > However, I think what you are suggesting is to disallow > mapping in interrupt context. This is a problem for zcache > as it already does mapping in interrupt context, namely for > page decompression in the page fault handler.
I don't get it. Page fault handler isn't interrupt context.
> > What do you think about making the per-cpu buffers local to > each zsmalloc pool? That way each user has their own per-cpu > buffers and don't step on each other's toes.
Maybe, It could be a solution if you really need it in interrupt context. But the concern is it could hurt zsmalloc's goal which is memory space efficiency if your system has lots of CPUs.
> > Thanks, > Seth > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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