On Sat, Jan 19, 2019 at 9:25 AM Jerry Hoemann <jerry.hoemann@xxxxxxx> wrote: > > On Tue, Jan 15, 2019 at 04:07:03PM +0800, Pingfan Liu wrote: > > People reported a bug on a high end server with many pcie devices, where > > kernel bootup with crashkernel=384M, and kaslr is enabled. Even > > though we still see much memory under 896 MB, the finding still failed > > intermittently. Because currently we can only find region under 896 MB, > > if without ',high' specified. Then KASLR breaks 896 MB into several parts > > randomly, and crashkernel reservation need be aligned to 128 MB, that's > > why failure is found. It raises confusion to the end user that sometimes > > crashkernel=X works while sometimes fails. > > If want to make it succeed, customer can change kernel option to > > "crashkernel=384M,high". Just this give "crashkernel=xx@yy" a very > > limited space to behave even though its grammar looks more generic. > > And we can't answer questions raised from customer that confidently: > > 1) why it doesn't succeed to reserve 896 MB; > > 2) what's wrong with memory region under 4G; > > 3) why I have to add ',high', I only require 384 MB, not 3840 MB. > > This patch tries to get memory region from 896 MB firstly, then [896MB,4G], > > finally above 4G. > > While allocating crashkernel from below 4G seems fine, won't we have > problems if the crash kernel gets allocated above 4G because of the SWIOTLB? > It will reserve extra memory below 4G for the swiotlb purpose. You can find the logic in reserve_crashkernel_low() And testing with crashkernel=512M@4G, we will get: cat /proc/iomem | grep Crash aa000000-b9ffffff : Crash kernel 100000000-11fffffff : Crash kernel Thanks, Pingfan > thanks > > > > Dave Young sent the original post, and I just re-post it with commit log > > improvement as his requirement. > > http://lists.infradead.org/pipermail/kexec/2017-October/019571.html > > There was an old discussion below (previously posted by Chao Wang): > > https://lkml.org/lkml/2013/10/15/601 > > > > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> > > Cc: Dave Young <dyoung@xxxxxxxxxx> > > Cc: Baoquan He <bhe@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> > > Cc: yinghai@xxxxxxxxxx, > > Cc: vgoyal@xxxxxxxxxx > > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > > --- > > v6 -> v7: fix spelling mistake pointed out by Randy > > arch/x86/kernel/setup.c | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > > index 3d872a5..fa62c81 100644 > > --- a/arch/x86/kernel/setup.c > > +++ b/arch/x86/kernel/setup.c > > @@ -551,6 +551,22 @@ static void __init reserve_crashkernel(void) > > high ? CRASH_ADDR_HIGH_MAX > > : CRASH_ADDR_LOW_MAX, > > crash_size, CRASH_ALIGN); > > +#ifdef CONFIG_X86_64 > > + /* > > + * crashkernel=X reserve below 896M fails? Try below 4G > > + */ > > + if (!high && !crash_base) > > + crash_base = memblock_find_in_range(CRASH_ALIGN, > > + (1ULL << 32), > > + crash_size, CRASH_ALIGN); > > + /* > > + * crashkernel=X reserve below 4G fails? Try MAXMEM > > + */ > > + if (!high && !crash_base) > > + crash_base = memblock_find_in_range(CRASH_ALIGN, > > + CRASH_ADDR_HIGH_MAX, > > + crash_size, CRASH_ALIGN); > > +#endif > > if (!crash_base) { > > pr_info("crashkernel reservation failed - No suitable area found.\n"); > > return; > > -- > > 2.7.4 > > > > > > _______________________________________________ > > kexec mailing list > > kexec@xxxxxxxxxxxxxxxxxxx > > http://lists.infradead.org/mailman/listinfo/kexec > > -- > > ----------------------------------------------------------------------------- > Jerry Hoemann Software Engineer Hewlett Packard Enterprise > ----------------------------------------------------------------------------- _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
