On Sat, Mar 05, 2022 at 02:19:41PM +0800, Tiezhu Yang wrote: > > > On 03/05/2022 01:05 AM, Maciej W. Rozycki wrote: > > On Wed, 2 Mar 2022, Tiezhu Yang wrote: > > > > > > As for memmap= option, it does not specify the memory map but rather alters > > > > the memory map passed by the firmware. Particularity in MIPS implementation > > > > it allows to add a single range of available or reserved memory. > > > > > > > > AFAIU, for the kdump use-case mem=X@Y should suffice. > > > > > > We can modify some code to make mem=X@Y work well, > > > but according to Documentation/admin-guide/kernel-parameters.txt, > > > the common way is mem=X and memmap=X@Y, so mem=X@Y for mips seems > > > odd, the intention of this patchset is to make mem= and memmap= > > > work well and consistent with the other archs. > > > > It is not the MIPS implementation that is odd, it is the others that have > > changed the semantics that are. > > > > When I added `mem=...' support to the MIPS platform, back on Dec 11th, > > 2000, which I needed for a system with with memory holes until I got > > proper memory probing implemented, AFAIR the only other implementation was > > for the x86 and naturally what I did for the MIPS platform was exactly the > > same. It used to be documented too, but the documentation was removed > > sometime back in 2003 when someone has changed the x86 semantics for > > reasons unknown to me and without letting people working on other > > platforms know, so things diverged. > > > > Please review: > > > > <https://lore.kernel.org/linux-mips/alpine.LFD.2.21.2010050133330.333514@xxxxxxxxxxxxxxxxxxxx/> > > > > as it has been already discussed. > > > > If you have a system that hangs with `mem=3G' and which does have > > contiguous RAM available for the kernel to use from 0 through to 3GiB, > > then please either bisect the problem or try finding the root cause as it > > used to work at least those 21 years ago. Conversely if your system does > > *not* have such RAM available, then use the correct option(s) instead that > > reflect your memory map. > > > > It is preferable that the memory map be determined automatically either > > by the firmware and then passed to the kernel somehow, or a device tree > > entry, or probed by the kernel itself. You shouldn't have to specify > > `mem=...' by hand except for debugging or as a temporary workaround. > > > > For example I have an x86 system that Linux does not how to interrogate > > for RAM beyond 64MiB, so I do use `memmap=128M@0' (for legacy reasons the > > x86 platform has a special exception to always exclude area between 640K > > and 1M from being used even if not explicitly specified, but we do not > > have a need for such legacy such legacy concerns with the MIPS port). I > > consider it an interim measure however until the kernel has been fixed. > > > > Maciej > > > > Hi Mike, Thomas and Maciej, > > Thank you very much for your feedbacks and discussions. > > To be frank, I think mem= and memmap= are used for debugging and testing > in most cases, the intention of this patchset is to refactor the related > code to make them work well on mips. mem= works fine on mips and there is no need to change it. If you must supply complex memory layout on the command line, consider implementing support for memmap=exact and multiple memmap= parameters on the kernel command line, like x86 does. > Now, if put the current patch #2 as the first patch, and then modify the > current patch #1 to support both mem=limit and mem=limit@base (if @base > is omitted, it is equivalent to mem=limit), the other patches #3 and #4 > remain unchanged, make sense? > > I will send v5 for your review. > > Thanks, > Tiezhu > -- Sincerely yours, Mike.
