> -----Original Message----- > From: Anshuman Khandual [mailto:anshuman.khandual@xxxxxxx] > Sent: Wednesday, July 8, 2020 4:18 PM > To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>; > akpm@xxxxxxxxxxxxxxxxxxxx > Cc: x86@xxxxxxxxxx; linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > Linuxarm <linuxarm@xxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > Roman Gushchin <guro@xxxxxx>; Catalin Marinas > <catalin.marinas@xxxxxxx>; Will Deacon <will@xxxxxxxxxx>; Thomas Gleixner > <tglx@xxxxxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; Borislav Petkov > <bp@xxxxxxxxx>; H . Peter Anvin <hpa@xxxxxxxxx>; Mike Kravetz > <mike.kravetz@xxxxxxxxxx>; Mike Rapoport <rppt@xxxxxxxxxxxxx>; Jonathan > Cameron <jonathan.cameron@xxxxxxxxxx> > Subject: Re: [PATCH] mm/hugetlb: split hugetlb_cma in nodes with memory > > Hello Barry, > > On 07/08/2020 05:53 AM, Barry Song wrote: > > Rather than splitting huge_cma in online nodes, it is better to do it in > > nodes with memory. > > Right, it makes sense to avoid nodes without memory, hence loosing portions > of CMA reservation intended for HugeTLB. N_MEMORY is better than > N_ONLINE > and will help avoid this situation. Thanks for taking a look, Anshuman. > > > For an ARM64 server with four numa nodes and only node0 has memory. If I > > set hugetlb_cma=4G in bootargs, > > > > without this patch, I got the below printk: > > hugetlb_cma: reserve 4096 MiB, up to 1024 MiB per node > > hugetlb_cma: reserved 1024 MiB on node 0 > > hugetlb_cma: reservation failed: err -12, node 1 > > hugetlb_cma: reservation failed: err -12, node 2 > > hugetlb_cma: reservation failed: err -12, node 3 > > As expected. > > > > > hugetlb_cma size is broken once the system has nodes without memory. > > I would not say that it is 'broken'. It is just not optimal but still works > as designed. > > > > > With this patch, I got the below printk: > > hugetlb_cma: reserve 4096 MiB, up to 4096 MiB per node > > hugetlb_cma: reserved 4096 MiB on node 0 > > As expected, the per node CMA reservation quota has changed from > N_ONLINE > to N_MEMORY. > > > > > So this patch fixes the broken hugetlb_cma size on arm64. > > There is nothing arm64 specific here. A platform where N_ONLINE != > N_MEMORY > i.e with some nodes without memory when CMA reservation gets called, will > have this problem. Agreed. one fact is that right now only x86 and arm64 are calling hugetlb_cma_reserve(). So I don't know how eager other platforms need this function. > > > > > Jonathan Cameron tested this patch on x86 platform. Jonathan figured out > x86 > > is much different with arm64. hugetlb_cma size has never broken on x86. > > On arm64 all nodes are marked online at the same time. On x86, only > > nodes with memory are initially marked as online: > > initmem_init()->x86_numa_init()->numa_init()-> > > numa_register_memblks()->alloc_node_data()->node_set_online() > > So at time of the existing cma setup call only the memory containing nodes > > are online. The other nodes are brought up much later. > > The problem is always there if N_ONLINE != N_MEMORY but in this case, it > is just hidden because N_ONLINE happen to match N_MEMORY during the > boot > process when hugetlb_cma_reserve() gets called. Yes. Exactly. > > > > > Thus, the change is simply to fix ARM64. A change is needed to x86 only > > because the inherent assumptions in cma_hugetlb_reserve() have changed. > > cma_hugetlb_reserve() will now scan over N_MEMORY and hence expects all > platforms to have N_MEMORY initialized properly before calling it. This > needs to be well documented for the hugetlb_cma_reserve() function along > with it's call sites. > Yep. will document this. > > > > Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages > using cma") > > I would not call this a "Fix". The current code still works, though in > a sub optimal manner. Do you think it is worth linux-stable? For example, is it better for this optimal manner to be in 5.7 and 5.8? or we have this patch in 5.9-rc1? To me, I would prefer 5.7 and 5.8 users can still have a hugetlb cma size which is consistent with the bootargs. > > > Cc: Roman Gushchin <guro@xxxxxx> > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > > Cc: Will Deacon <will@xxxxxxxxxx> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > > Cc: Borislav Petkov <bp@xxxxxxxxx> > > Cc: H. Peter Anvin <hpa@xxxxxxxxx> > > Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> > > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> > > Cc: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx> > > Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx> > > --- > > arch/arm64/mm/init.c | 18 +++++++++--------- > > arch/x86/kernel/setup.c | 13 ++++++++++--- > > mm/hugetlb.c | 4 ++-- > > 3 files changed, 21 insertions(+), 14 deletions(-) > > > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > > index 1e93cfc7c47a..f6090ef6812b 100644 > > --- a/arch/arm64/mm/init.c > > +++ b/arch/arm64/mm/init.c > > @@ -420,15 +420,6 @@ void __init bootmem_init(void) > > > > arm64_numa_init(); > > > > - /* > > - * must be done after arm64_numa_init() which calls numa_init() to > > - * initialize node_online_map that gets used in hugetlb_cma_reserve() > > - * while allocating required CMA size across online nodes. > > - */ > > -#ifdef CONFIG_ARM64_4K_PAGES > > - hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT); > > -#endif > > - > > /* > > * Sparsemem tries to allocate bootmem in memory_present(), so must > be > > * done after the fixed reservations. > > @@ -438,6 +429,15 @@ void __init bootmem_init(void) > > sparse_init(); > > zone_sizes_init(min, max); > > > > + /* > > + * must be done after zone_sizes_init() which calls node_set_state() to > > + * setup node_states[N_MEMORY] that gets used in > hugetlb_cma_reserve() > > + * while allocating required CMA size across nodes with memory. > > + */ > > Needs better wording here, in particular a reference to free_area_init() > that updates N_MEMORY via node_set_state(). Also mention the fact that > now hugetlb_cma_reserve() scans over N_MEMORY nodemask and hence > expects > the platforms to have a properly initialized one. Ok. free_area_init() needs to be highlighted. > > > +#ifdef CONFIG_ARM64_4K_PAGES > > + hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT); > > +#endif > > + > > memblock_dump_all(); > > } > > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > > index a3767e74c758..fdb3a934b6c6 100644 > > --- a/arch/x86/kernel/setup.c > > +++ b/arch/x86/kernel/setup.c > > @@ -1164,9 +1164,6 @@ void __init setup_arch(char **cmdline_p) > > initmem_init(); > > dma_contiguous_reserve(max_pfn_mapped << PAGE_SHIFT); > > > > - if (boot_cpu_has(X86_FEATURE_GBPAGES)) > > - hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT); > > - > > /* > > * Reserve memory for crash kernel after SRAT is parsed so that it > > * won't consume hotpluggable memory. > > @@ -1180,6 +1177,16 @@ void __init setup_arch(char **cmdline_p) > > > > x86_init.paging.pagetable_init(); > > > > + /* > > + * must be done after zone_sizes_init() which calls node_set_state() to > > + * setup node_states[N_MEMORY] that gets used in > hugetlb_cma_reserve() > > + * while allocating required CMA size across nodes with memory. > > + * And zone_sizes_init() is done in x86_init.paging.pagetable_init() > > + * which is typically paging_init(). > > + */ > > Drop the last sentence here. Should have just the same comment as arm64. Do we need something to explain why x86_init.paging.pagetable_init() can do free_area_init()? > > > + if (boot_cpu_has(X86_FEATURE_GBPAGES)) > > + hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT); > > + > > kasan_init(); > > > > /* > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index d293c823121e..3a0ad49187e4 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -5699,12 +5699,12 @@ void __init hugetlb_cma_reserve(int order) > > * If 3 GB area is requested on a machine with 4 numa nodes, > > * let's allocate 1 GB on first three nodes and ignore the last one. > > */ > > - per_node = DIV_ROUND_UP(hugetlb_cma_size, nr_online_nodes); > > + per_node = DIV_ROUND_UP(hugetlb_cma_size, > num_node_state(N_MEMORY)); > > pr_info("hugetlb_cma: reserve %lu MiB, up to %lu MiB per node\n", > > hugetlb_cma_size / SZ_1M, per_node / SZ_1M); > > > > reserved = 0; > > - for_each_node_state(nid, N_ONLINE) { > > + for_each_node_state(nid, N_MEMORY) { > > int res; > > > > size = min(per_node, hugetlb_cma_size - reserved); > > > > The patch makes sense. But it needs better articulation of the problem in > the commit message, specifically pointing out the fact that it originates > primarily from a scenario where N_ONLINE != N_MEMORY because the > presence > of memory less online nodes. It manifests itself on arm64 because of how > N_ONLINE and N_MEMORY gets initialized during boot but remains hidden on > x86 for the very same reason. Thanks Barry
