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    SubjectRe: [this_cpu_xx V4 12/20] Move early initialization of pagesets out of zone_wait_table_init()
    On Thu, Oct 01, 2009 at 05:25:33PM -0400, cl@linux-foundation.org wrote:
    > Explicitly initialize the pagesets after the per cpu areas have been
    > initialized. This is necessary in order to be able to use per cpu
    > operations in later patches.
    >

    Can you be more explicit about this? I think the reasoning is as follows

    A later patch will use DEFINE_PER_CPU which allocates memory later in
    the boot-cycle after zones have already been initialised. Without this
    patch, use of DEFINE_PER_CPU would result in invalid memory accesses
    during pageset initialisation.

    Have another question below as well.

    > Cc: Mel Gorman <mel@csn.ul.ie>
    > Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
    >
    > ---
    > arch/ia64/kernel/setup.c | 1 +
    > arch/powerpc/kernel/setup_64.c | 1 +
    > arch/sparc/kernel/smp_64.c | 1 +
    > arch/x86/kernel/setup_percpu.c | 2 ++
    > include/linux/mm.h | 1 +
    > mm/page_alloc.c | 40 +++++++++++++++++++++++++++++-----------
    > mm/percpu.c | 2 ++
    > 7 files changed, 37 insertions(+), 11 deletions(-)
    >
    > Index: linux-2.6/mm/page_alloc.c
    > ===================================================================
    > --- linux-2.6.orig/mm/page_alloc.c 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/mm/page_alloc.c 2009-10-01 09:36:19.000000000 -0500
    > @@ -3270,23 +3270,42 @@ void zone_pcp_update(struct zone *zone)
    > stop_machine(__zone_pcp_update, zone, NULL);
    > }
    >
    > -static __meminit void zone_pcp_init(struct zone *zone)
    > +/*
    > + * Early setup of pagesets.
    > + *
    > + * In the NUMA case the pageset setup simply results in all zones pcp
    > + * pointer being directed at a per cpu pageset with zero batchsize.
    > + *

    The batchsize becomes 1, not 0 if you look at setup_pageset() but that aside,
    it's unclear from the comment *why* the batchsize is 1 in the NUMA case.
    Maybe something like the following?

    =====
    In the NUMA case, the boot_pageset is used until the slab allocator is
    available to allocate per-zone pagesets as each CPU is brought up. At
    this point, the batchsize is set to 1 to prevent pages "leaking" onto the
    boot_pageset freelists.
    =====

    Otherwise, nothing in the patch jumped out at me other than to double
    check CPU-up events actually result in process_zones() being called and
    that boot_pageset is not being accidentally used in the long term.

    > + * This means that every free and every allocation occurs directly from
    > + * the buddy allocator tables.
    > + *
    > + * The pageset never queues pages during early boot and is therefore usable
    > + * for every type of zone.
    > + */
    > +__meminit void setup_pagesets(void)
    > {
    > int cpu;
    > - unsigned long batch = zone_batchsize(zone);
    > + struct zone *zone;
    >
    > - for (cpu = 0; cpu < NR_CPUS; cpu++) {
    > + for_each_zone(zone) {
    > #ifdef CONFIG_NUMA
    > - /* Early boot. Slab allocator not functional yet */
    > - zone_pcp(zone, cpu) = &boot_pageset[cpu];
    > - setup_pageset(&boot_pageset[cpu],0);
    > + unsigned long batch = 0;
    > +
    > + for (cpu = 0; cpu < NR_CPUS; cpu++) {
    > + /* Early boot. Slab allocator not functional yet */
    > + zone_pcp(zone, cpu) = &boot_pageset[cpu];
    > + }
    > #else
    > - setup_pageset(zone_pcp(zone,cpu), batch);
    > + unsigned long batch = zone_batchsize(zone);
    > #endif
    > +
    > + for_each_possible_cpu(cpu)
    > + setup_pageset(zone_pcp(zone, cpu), batch);
    > +
    > + if (zone->present_pages)
    > + printk(KERN_DEBUG " %s zone: %lu pages, LIFO batch:%lu\n",
    > + zone->name, zone->present_pages, batch);
    > }
    > - if (zone->present_pages)
    > - printk(KERN_DEBUG " %s zone: %lu pages, LIFO batch:%lu\n",
    > - zone->name, zone->present_pages, batch);
    > }
    >
    > __meminit int init_currently_empty_zone(struct zone *zone,
    > @@ -3841,7 +3860,6 @@ static void __paginginit free_area_init_
    >
    > zone->prev_priority = DEF_PRIORITY;
    >
    > - zone_pcp_init(zone);
    > for_each_lru(l) {
    > INIT_LIST_HEAD(&zone->lru[l].list);
    > zone->reclaim_stat.nr_saved_scan[l] = 0;
    > Index: linux-2.6/include/linux/mm.h
    > ===================================================================
    > --- linux-2.6.orig/include/linux/mm.h 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/include/linux/mm.h 2009-10-01 09:36:19.000000000 -0500
    > @@ -1060,6 +1060,7 @@ extern void show_mem(void);
    > extern void si_meminfo(struct sysinfo * val);
    > extern void si_meminfo_node(struct sysinfo *val, int nid);
    > extern int after_bootmem;
    > +extern void setup_pagesets(void);
    >
    > #ifdef CONFIG_NUMA
    > extern void setup_per_cpu_pageset(void);
    > Index: linux-2.6/arch/ia64/kernel/setup.c
    > ===================================================================
    > --- linux-2.6.orig/arch/ia64/kernel/setup.c 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/arch/ia64/kernel/setup.c 2009-10-01 09:35:39.000000000 -0500
    > @@ -864,6 +864,7 @@ void __init
    > setup_per_cpu_areas (void)
    > {
    > /* start_kernel() requires this... */
    > + setup_pagesets();
    > }
    > #endif
    >
    > Index: linux-2.6/arch/powerpc/kernel/setup_64.c
    > ===================================================================
    > --- linux-2.6.orig/arch/powerpc/kernel/setup_64.c 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/arch/powerpc/kernel/setup_64.c 2009-10-01 09:35:39.000000000 -0500
    > @@ -578,6 +578,7 @@ static void ppc64_do_msg(unsigned int sr
    > snprintf(buf, 128, "%s", msg);
    > ppc_md.progress(buf, 0);
    > }
    > + setup_pagesets();
    > }
    >
    > /* Print a boot progress message. */
    > Index: linux-2.6/arch/sparc/kernel/smp_64.c
    > ===================================================================
    > --- linux-2.6.orig/arch/sparc/kernel/smp_64.c 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/arch/sparc/kernel/smp_64.c 2009-10-01 09:35:39.000000000 -0500
    > @@ -1486,4 +1486,5 @@ void __init setup_per_cpu_areas(void)
    > of_fill_in_cpu_data();
    > if (tlb_type == hypervisor)
    > mdesc_fill_in_cpu_data(cpu_all_mask);
    > + setup_pagesets();
    > }
    > Index: linux-2.6/arch/x86/kernel/setup_percpu.c
    > ===================================================================
    > --- linux-2.6.orig/arch/x86/kernel/setup_percpu.c 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/arch/x86/kernel/setup_percpu.c 2009-10-01 09:35:39.000000000 -0500
    > @@ -269,4 +269,6 @@ void __init setup_per_cpu_areas(void)
    >
    > /* Setup cpu initialized, callin, callout masks */
    > setup_cpu_local_masks();
    > +
    > + setup_pagesets();
    > }
    > Index: linux-2.6/mm/percpu.c
    > ===================================================================
    > --- linux-2.6.orig/mm/percpu.c 2009-10-01 08:54:19.000000000 -0500
    > +++ linux-2.6/mm/percpu.c 2009-10-01 09:35:39.000000000 -0500
    > @@ -2062,5 +2062,7 @@ void __init setup_per_cpu_areas(void)
    > delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
    > for_each_possible_cpu(cpu)
    > __per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];
    > +
    > + setup_pagesets();
    > }
    > #endif /* CONFIG_HAVE_SETUP_PER_CPU_AREA */
    >
    > --
    > --
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    >

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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