On Mon, Jan 07, 2019 at 04:04:59PM +0800, Pingfan Liu wrote: > Customer 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 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. 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 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. > > This patch simplifies the method suggested in the mail [1]. It just goes > bottom-up to find a candidate region for crashkernel. The bottom-up may be > better compatible with the old reservation style, i.e. still want to get > memory region from 896 MB firstly, then [896 MB, 4G], finally above 4G. > > 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. > > [1]: http://lists.infradead.org/pipermail/kexec/2017-October/019571.html > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> > Cc: Tang Chen <tangchen@xxxxxxxxxxxxxx> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> > Cc: Len Brown <lenb@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Yaowei Bai <baiyaowei@xxxxxxxxxxxxxxxxxxxx> > Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Cc: Nicholas Piggin <npiggin@xxxxxxxxx> > Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Cc: Daniel Vacek <neelx@xxxxxxxxxx> > Cc: Mathieu Malaterre <malat@xxxxxxxxxx> > Cc: Stefan Agner <stefan@xxxxxxxx> > Cc: Dave Young <dyoung@xxxxxxxxxx> > Cc: Baoquan He <bhe@xxxxxxxxxx> > Cc: yinghai@xxxxxxxxxx, > Cc: vgoyal@xxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > --- > v4 -> v5: > add a wrapper of bottom up allocation func > v3 -> v4: > instead of exporting the stage of parsing mem hotplug info, just using the bottom-up allocation func directly > arch/x86/kernel/setup.c | 8 ++++---- > include/linux/memblock.h | 3 +++ > mm/memblock.c | 29 +++++++++++++++++++++++++++++ > 3 files changed, 36 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index d494b9b..80e7923 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -546,10 +546,10 @@ static void __init reserve_crashkernel(void) > * 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); > + crash_base = memblock_find_range_bottom_up(CRASH_ALIGN, > + (max_pfn * PAGE_SIZE), crash_size, CRASH_ALIGN, > + NUMA_NO_NODE); > + > if (!crash_base) { > pr_info("crashkernel reservation failed - No suitable area found.\n"); > return; > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > index aee299a..a35ae17 100644 > --- a/include/linux/memblock.h > +++ b/include/linux/memblock.h > @@ -116,6 +116,9 @@ phys_addr_t memblock_find_in_range_node(phys_addr_t size, phys_addr_t align, > int nid, enum memblock_flags flags); > phys_addr_t memblock_find_in_range(phys_addr_t start, phys_addr_t end, > phys_addr_t size, phys_addr_t align); > +phys_addr_t __init_memblock > +memblock_find_range_bottom_up(phys_addr_t start, phys_addr_t end, > + phys_addr_t size, phys_addr_t align, int nid); > void memblock_allow_resize(void); > int memblock_add_node(phys_addr_t base, phys_addr_t size, int nid); > int memblock_add(phys_addr_t base, phys_addr_t size); > diff --git a/mm/memblock.c b/mm/memblock.c > index 81ae63c..f68287e 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -192,6 +192,35 @@ __memblock_find_range_bottom_up(phys_addr_t start, phys_addr_t end, > return 0; > } > > +phys_addr_t __init_memblock > +memblock_find_range_bottom_up(phys_addr_t start, phys_addr_t end, > + phys_addr_t size, phys_addr_t align, int nid) > +{ > + phys_addr_t ret; > + enum memblock_flags flags = choose_memblock_flags(); > + > + /* pump up @end */ > + if (end == MEMBLOCK_ALLOC_ACCESSIBLE) > + end = memblock.current_limit; > + > + /* avoid allocating the first page */ > + start = max_t(phys_addr_t, start, PAGE_SIZE); > + end = max(start, end); > + > +again: > + ret = __memblock_find_range_bottom_up(start, end, size, align, > + nid, flags); > + > + if (!ret && (flags & MEMBLOCK_MIRROR)) { > + pr_warn("Could not allocate %pap bytes of mirrored memory\n", > + &size); > + flags &= ~MEMBLOCK_MIRROR; > + goto again; > + } I'm not thrilled by duplicating this code (yet again). I liked the v3 of this patch [1] more, assuming we allow bottom-up mode to allocate [0, kernel_start) unconditionally. I'd just replace you first patch in v3 [2] with something like: diff --git a/mm/memblock.c b/mm/memblock.c index 7df468c..d1b30b9 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -274,24 +274,14 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size, * try bottom-up allocation only when bottom-up mode * is set and @end is above the kernel image. */ - if (memblock_bottom_up() && end > kernel_end) { - phys_addr_t bottom_up_start; - - /* make sure we will allocate above the kernel */ - bottom_up_start = max(start, kernel_end); - + if (memblock_bottom_up()) { /* ok, try bottom-up allocation first */ - ret = __memblock_find_range_bottom_up(bottom_up_start, end, + ret = __memblock_find_range_bottom_up(start, end, size, align, nid, flags); if (ret) return ret; /* - * we always limit bottom-up allocation above the kernel, - * but top-down allocation doesn't have the limit, so - * retrying top-down allocation may succeed when bottom-up - * allocation failed. - * * bottom-up allocation is expected to be fail very rarely, * so we use WARN_ONCE() here to see the stack trace if * fail happens. [1] https://lore.kernel.org/lkml/1545966002-3075-3-git-send-email-kernelfans@xxxxxxxxx/ [2] https://lore.kernel.org/lkml/1545966002-3075-2-git-send-email-kernelfans@xxxxxxxxx/ > + > + return ret; > +} > + > /** > * __memblock_find_range_top_down - find free area utility, in top-down > * @start: start of candidate range > -- > 2.7.4 > -- Sincerely yours, Mike.
