On 12/15/21 at 11:01am, Catalin Marinas wrote: > On Wed, Dec 15, 2021 at 11:42:19AM +0800, Baoquan He wrote: > > On 12/14/21 at 07:24pm, Catalin Marinas wrote: > > > On Tue, Dec 14, 2021 at 08:07:58PM +0100, Borislav Petkov wrote: > > > > On Fri, Dec 10, 2021 at 02:55:25PM +0800, Zhen Lei wrote: > > > > > From: Chen Zhou <chenzhou10@xxxxxxxxxx> > > > > > > > > > > The lower bounds of crash kernel reservation and crash kernel low > > > > > reservation are different, use the consistent value CRASH_ALIGN. > > > > > > > > A big WHY is missing here to explain why the lower bound of the > > > > allocation range needs to be 16M and why was 0 wrong? > > > > > > I asked the same here: > > > > > > https://lore.kernel.org/r/20210224143547.GB28965@xxxxxxx > > > > > > IIRC Baoquan said that there is a 1MB reserved for x86 anyway in the > > > lower part, so that's equivalent in practice to starting from > > > CRASH_ALIGN. > > > > Yeah, even for i386, there's area reserved by BIOS inside low 1M. > > Considering the existing alignment CRASH_ALIGN which is 16M, we > > definitely have no chance to get memory starting from 0. So starting > > from 16M can skip the useless memblock searching, and make the > > crashkernel low reservation consisten with crashkernel reservation on > > allocation code. > > That's the x86 assumption. Is it valid for other architectures once the > code has been made generic in patch 6? It should be ok for arm64, RAM > tends to start from higher up but other architectures may start using > this common code. Good point. I didn't think of this from generic code side, then let's keep it as 0. > > If you want to keep the same semantics as before, just leave it as 0. > It's not that the additional lower bound makes the search slower. Agree.
