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    SubjectRe: [GIT PULL] scheduler fixes


    On Mon, 25 May 2009, Pekka J Enberg wrote:
    > diff --git a/init/main.c b/init/main.c
    > index 33ce929..fb0e004 100644
    > --- a/init/main.c
    > +++ b/init/main.c
    > @@ -576,6 +576,22 @@ asmlinkage void __init start_kernel(void)
    > setup_nr_cpu_ids();
    > smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
    >
    > + build_all_zonelists();
    > + page_alloc_init();
    > +
    > + printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
    > + parse_early_param();
    > + parse_args("Booting kernel", static_command_line, __start___param,
    > + __stop___param - __start___param,
    > + &unknown_bootoption);
    > + pidhash_init();
    > + vmalloc_init();
    > + vfs_caches_init_early();
    > + /*
    > + * Set up kernel memory allocators
    > + */
    > + mem_init();
    > + kmem_cache_init();

    So what strikes me is a question:

    - why do we want to do pidhash_init and vfs_caches_init_early() so early?

    Yes, pidhash_init() now uses alloc_bootmem. It's an allocation that is not
    trivially small, but it's not humongous either (max 4096 hash list heads,
    one pointer each).

    And vfs_caches_init_early() is actually doing some rather strange things,
    like doing a "alloc_large_system_hash()" but not unconditionally: it does
    it in the "late" initialization too, if not done early. inode_init_early
    does soemthing very similar (ie a _conditional_ early init).

    So none of this seems to really get a huge advantage from the early init.
    There seems to be some subtle NUMA issues, but do we really want that? I
    get the feeling that nobody ever wanted to do it early, and then the NUMA
    people said "I don't wnt to do this early, but I don't want to touch the
    non-NUMA case, so I'll do it early for non-numa, and late for numa".

    I'm also not entirely sure we really need to do vmalloc_init() that early,
    but I dunno. It also uses alloc_bootmem().

    Linus


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