Hi Baoquan, Thanks for your kindly review. I will update the commit log to explain the scenario. Best regards, Pingfan On Wed, Dec 12, 2018 at 5:01 PM Baoquan He <bhe@xxxxxxxxxx> wrote: > > Hi Pingfan, > > Thanks for fixing this. > > On 12/12/18 at 04:19pm, Pingfan Liu wrote: > > I encounter a case where crashkernel=384M, and kaslr is enabled. During the > > test, sometimes, the system may fail to reserve region for crash kernel, > > although there is much free space above 896MB. It is caused by the > > I remember this bug was reported by our customer. They specify > crashkernel=384MB on a high end server with many pcie devices. 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 w/0 ',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. > > 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 grammer 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. > > > truncation of the candidate region by kaslr kernel. It raises confusion to > > the end user that sometimes crashkernel=X works while sometimes fails. > > Since on x86, kaslr is a default option, and this corner case is > > unavoidable. > > This patch simplifies the method suggested in the mail [1]. It just goes > > bottom-up to find a candidate region for crashkernel. > > There is one trivial thing about the compatibility with old kexec-tools: > > if the reserved region is above 896M, then old tool will fail to load > > bzImage. But without this patch, the old tool also fail since there is no > > memory below 896M can be reserved for crashkernel. > > Meanwhile, we set bottom-up to try to reserve crashkernel because we > still want to get memory region from 896 MB firstly, then [896 MB, 4G], > finally above 4G. This gives us a chance to be compatible with the old > reservation style, and this is what we have been doing in redhat > distros. We may only search [128MB, 4G] only if people mind, just leave > above 4G reservation to ',high' explicitly. > > Thanks > Baoquan > > > > [1]: http://lists.infradead.org/pipermail/kexec/2017-October/019571.html > > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> > > Cc: Dave Young <dyoung@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Baoquan He <bhe@xxxxxxxxxx> > > Cc: yinghai@xxxxxxxxxx, > > Cc: vgoyal@xxxxxxxxxx > > Cc: kexec@xxxxxxxxxxxxxxxxxxx > > > > --- > > arch/x86/kernel/setup.c | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > > index d494b9b..60f12c4 100644 > > --- a/arch/x86/kernel/setup.c > > +++ b/arch/x86/kernel/setup.c > > @@ -541,15 +541,18 @@ static void __init reserve_crashkernel(void) > > > > /* 0 means: find the address automatically */ > > if (crash_base <= 0) { > > + if (!memblock_bottom_up()) > > + memblock_set_bottom_up(true); > Here maybe change it like below. Just personal opinion, not a big deal, > not strongly suggested. > bool bottom_up; > > bottom_up = memblock_bottom_up(); > memblock_set_bottom_up(true); > > > /* > > * Set CRASH_ADDR_LOW_MAX upper bound for crash memory, > > * as old kexec-tools loads bzImage below that, unless > > * "crashkernel=size[KMG],high" is specified. > > */ > > crash_base = memblock_find_in_range(CRASH_ALIGN, > > - high ? CRASH_ADDR_HIGH_MAX > > - : CRASH_ADDR_LOW_MAX, > > - crash_size, CRASH_ALIGN); > > + (max_pfn * PAGE_SIZE), crash_size, CRASH_ALIGN); > memblock_set_bottom_up(bottom_up); > > + > > 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
