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. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
