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Message-ID: <50C0D189.7020306@gmail.com> Date: Fri, 07 Dec 2012 01:10:33 +0800 From: Jiang Liu <liuj97@...il.com> To: "Rafael J. Wysocki" <rjw@...k.pl> CC: Toshi Kani <toshi.kani@...com>, linux-acpi@...r.kernel.org, Hanjun Guo <guohanjun@...wei.com>, Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>, isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com, lenb@...nel.org, gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Tang Chen <tangchen@...fujitsu.com> Subject: Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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