On 11/30/2012 05:25 AM, Rafael J. Wysocki wrote: > On Thursday, November 29, 2012 01:56:17 PM Toshi Kani wrote: >> On Thu, 2012-11-29 at 13:39 -0700, Toshi Kani wrote: >>> On Thu, 2012-11-29 at 21:30 +0100, Rafael J. Wysocki wrote: >>>> On Thursday, November 29, 2012 10:03:12 AM Toshi Kani wrote: >>>>> On Thu, 2012-11-29 at 11:15 +0100, Rafael J. Wysocki wrote: >>>>>> On Wednesday, November 28, 2012 11:41:36 AM Toshi Kani wrote: >>>>>>> 1. Validate phase - Verify if the request is a supported operation. All >>>>>>> known restrictions are verified at this phase. For instance, if a >>>>>>> hot-remove request involves kernel memory, it is failed in this phase. >>>>>>> Since this phase makes no change, no rollback is necessary to fail. >>>>>> >>>>>> Actually, we can't do it this way, because the conditions may change between >>>>>> the check and the execution. So the first phase needs to involve execution >>>>>> to some extent, although only as far as it remains reversible. >>>>> >>>>> For memory hot-remove, we can check if the target memory ranges are >>>>> within ZONE_MOVABLE. We should not allow user to change this setup >>>>> during hot-remove operation. Other things may be to check if a target >>>>> node contains cpu0 (until it is supported), the console UART (assuming >>>>> we cannot delete it), etc. We should avoid doing rollback as much as we >>>>> can. >>>> >>>> Yes, we can make some checks upfront as an optimization and fail early if >>>> the conditions are not met, but for correctness we need to repeat those >>>> checks later anyway. Once we've decided to go for the eject, the conditions >>>> must hold whatever happens. >>> >>> Agreed. >> >> BTW, it is not an optimization I am after for this phase. There are >> many error cases during hot-plug operations. It is difficult to assure >> that rollback is successful for every error condition in terms of >> testing and maintaining the code. So, it is easier to fail beforehand >> when possible. > > OK, but as I said it is necessary to ensure that the conditions will be met > in the next phases as well if we don't fail. Yes, that's absolutely an requirement. Otherwise QA people will call you when doing stress tests. > > Thanks, > Rafael > > -- 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>