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    SubjectRe: speed difference between using hard-linked and modular drives?
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       From: Anton Blanchard <anton@samba.org>
    Date: Sat, 10 Nov 2001 15:56:03 +1100

    You can see the average depth of the get_free_page hash is way too deep.
    I agree there are a lot of pagecache pages (17GB in the gfp test and 21GB
    in the vmalloc test), but we have to make use of the 32GB of RAM :)

    Anton, are you bored? :-) If so, could you test out the patch
    below on your ppc64 box? It does the "page hash table via bootmem"
    thing. It is against 2.4.15-pre2

    The ppc64 specific bits you'll need to do, but they should
    be very straight forward.

    It also fixes a really stupid bug in the bootmem allocator.
    If the bootmem area starts in some unaligned address, the
    "align" argument to the bootmem allocator isn't honored.

    --- ./arch/alpha/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/alpha/mm/init.c Sat Nov 10 01:49:56 2001
    @@ -23,6 +23,7 @@
    #ifdef CONFIG_BLK_DEV_INITRD
    #include <linux/blk.h>
    #endif
    +#include <linux/pagemap.h>

    #include <asm/system.h>
    #include <asm/uaccess.h>
    @@ -360,6 +361,7 @@
    mem_init(void)
    {
    max_mapnr = num_physpages = max_low_pfn;
    + page_cache_init(count_free_bootmem());
    totalram_pages += free_all_bootmem();
    high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);

    --- ./arch/alpha/mm/numa.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/alpha/mm/numa.c Sat Nov 10 01:52:27 2001
    @@ -15,6 +15,7 @@
    #ifdef CONFIG_BLK_DEV_INITRD
    #include <linux/blk.h>
    #endif
    +#include <linux/pagemap.h>

    #include <asm/hwrpb.h>
    #include <asm/pgalloc.h>
    @@ -359,8 +360,13 @@
    extern char _text, _etext, _data, _edata;
    extern char __init_begin, __init_end;
    extern unsigned long totalram_pages;
    - unsigned long nid, i;
    + unsigned long nid, i, num_free_bootmem_pages;
    mem_map_t * lmem_map;
    +
    + num_free_bootmem_pages = 0;
    + for (nid = 0; nid < numnodes; nid++)
    + num_free_bootmem_pages += count_free_bootmem_node(NODE_DATA(nid));
    + page_cache_init(num_free_bootmem_pages);

    high_memory = (void *) __va(max_mapnr <<PAGE_SHIFT);

    --- ./arch/arm/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/arm/mm/init.c Sat Nov 10 01:52:34 2001
    @@ -23,6 +23,7 @@
    #include <linux/init.h>
    #include <linux/bootmem.h>
    #include <linux/blk.h>
    +#include <linux/pagemap.h>

    #include <asm/segment.h>
    #include <asm/mach-types.h>
    @@ -594,6 +595,7 @@
    void __init mem_init(void)
    {
    unsigned int codepages, datapages, initpages;
    + unsigned long num_free_bootmem_pages;
    int i, node;

    codepages = &_etext - &_text;
    @@ -608,6 +610,11 @@
    */
    if (meminfo.nr_banks != 1)
    create_memmap_holes(&meminfo);
    +
    + num_free_bootmem_pages = 0;
    + for (node = 0; node < numnodes; node++)
    + num_free_bootmem_pages += count_free_bootmem_node(NODE_DATA(node));
    + page_cache_init(num_free_bootmem_pages);

    /* this will put all unused low memory onto the freelists */
    for (node = 0; node < numnodes; node++) {
    --- ./arch/i386/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/i386/mm/init.c Sat Nov 10 01:53:43 2001
    @@ -455,6 +455,8 @@
    #endif
    high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);

    + page_cache_init(count_free_bootmem());
    +
    /* clear the zero-page */
    memset(empty_zero_page, 0, PAGE_SIZE);

    --- ./arch/m68k/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/m68k/mm/init.c Sat Nov 10 01:54:47 2001
    @@ -20,6 +20,7 @@
    #ifdef CONFIG_BLK_DEV_RAM
    #include <linux/blk.h>
    #endif
    +#include <linux/pagemap.h>

    #include <asm/setup.h>
    #include <asm/uaccess.h>
    @@ -135,6 +136,8 @@
    if (MACH_IS_ATARI)
    atari_stram_mem_init_hook();
    #endif
    +
    + page_cache_init(count_free_bootmem());

    /* this will put all memory onto the freelists */
    totalram_pages = free_all_bootmem();
    --- ./arch/mips/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/mips/mm/init.c Sat Nov 10 01:55:09 2001
    @@ -28,6 +28,7 @@
    #ifdef CONFIG_BLK_DEV_INITRD
    #include <linux/blk.h>
    #endif
    +#include <linux/pagemap.h>

    #include <asm/bootinfo.h>
    #include <asm/cachectl.h>
    @@ -203,6 +204,8 @@

    max_mapnr = num_physpages = max_low_pfn;
    high_memory = (void *) __va(max_mapnr << PAGE_SHIFT);
    +
    + page_cache_init(count_free_bootmem());

    totalram_pages += free_all_bootmem();
    totalram_pages -= setup_zero_pages(); /* Setup zeroed pages. */
    --- ./arch/ppc/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/ppc/mm/init.c Sat Nov 10 01:57:34 2001
    @@ -34,6 +34,7 @@
    #ifdef CONFIG_BLK_DEV_INITRD
    #include <linux/blk.h> /* for initrd_* */
    #endif
    +#include <linux/pagemap.h>

    #include <asm/pgalloc.h>
    #include <asm/prom.h>
    @@ -462,6 +463,8 @@

    high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
    num_physpages = max_mapnr; /* RAM is assumed contiguous */
    +
    + page_cache_init(count_free_bootmem());

    totalram_pages += free_all_bootmem();

    --- ./arch/sparc/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/sparc/mm/init.c Sat Nov 10 01:59:48 2001
    @@ -25,6 +25,7 @@
    #include <linux/init.h>
    #include <linux/highmem.h>
    #include <linux/bootmem.h>
    +#include <linux/pagemap.h>

    #include <asm/system.h>
    #include <asm/segment.h>
    @@ -434,6 +435,8 @@

    max_mapnr = last_valid_pfn - (phys_base >> PAGE_SHIFT);
    high_memory = __va(max_low_pfn << PAGE_SHIFT);
    +
    + page_cache_init(count_free_bootmem());

    #ifdef DEBUG_BOOTMEM
    prom_printf("mem_init: Calling free_all_bootmem().\n");
    --- ./arch/sparc64/mm/init.c.~1~ Fri Nov 9 18:42:08 2001
    +++ ./arch/sparc64/mm/init.c Sat Nov 10 02:00:23 2001
    @@ -16,6 +16,7 @@
    #include <linux/blk.h>
    #include <linux/swap.h>
    #include <linux/swapctl.h>
    +#include <linux/pagemap.h>

    #include <asm/head.h>
    #include <asm/system.h>
    @@ -1584,6 +1585,8 @@

    max_mapnr = last_valid_pfn - (phys_base >> PAGE_SHIFT);
    high_memory = __va(last_valid_pfn << PAGE_SHIFT);
    +
    + page_cache_init(count_free_bootmem());

    num_physpages = free_all_bootmem() - 1;

    --- ./arch/sh/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/sh/mm/init.c Sat Nov 10 01:59:56 2001
    @@ -26,6 +26,7 @@
    #endif
    #include <linux/highmem.h>
    #include <linux/bootmem.h>
    +#include <linux/pagemap.h>

    #include <asm/processor.h>
    #include <asm/system.h>
    @@ -139,6 +140,7 @@
    void __init mem_init(void)
    {
    extern unsigned long empty_zero_page[1024];
    + unsigned long num_free_bootmem_pages;
    int codesize, reservedpages, datasize, initsize;
    int tmp;

    @@ -148,6 +150,12 @@
    /* clear the zero-page */
    memset(empty_zero_page, 0, PAGE_SIZE);
    __flush_wback_region(empty_zero_page, PAGE_SIZE);
    +
    + num_free_bootmem_pages = count_free_bootmem_node(NODE_DATA(0));
    +#ifdef CONFIG_DISCONTIGMEM
    + num_free_bootmem_pages += count_free_bootmem_node(NODE_DATA(1));
    +#endif
    + page_cache_init(num_free_bootmem_pages);

    /* this will put all low memory onto the freelists */
    totalram_pages += free_all_bootmem_node(NODE_DATA(0));
    --- ./arch/s390/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/s390/mm/init.c Sat Nov 10 01:57:56 2001
    @@ -186,6 +186,8 @@
    /* clear the zero-page */
    memset(empty_zero_page, 0, PAGE_SIZE);

    + page_cache_init(count_free_bootmem());
    +
    /* this will put all low memory onto the freelists */
    totalram_pages += free_all_bootmem();

    --- ./arch/ia64/mm/init.c.~1~ Fri Nov 9 19:08:02 2001
    +++ ./arch/ia64/mm/init.c Sat Nov 10 01:54:20 2001
    @@ -13,6 +13,7 @@
    #include <linux/reboot.h>
    #include <linux/slab.h>
    #include <linux/swap.h>
    +#include <linux/pagemap.h>

    #include <asm/bitops.h>
    #include <asm/dma.h>
    @@ -406,6 +407,8 @@

    max_mapnr = max_low_pfn;
    high_memory = __va(max_low_pfn * PAGE_SIZE);
    +
    + page_cache_init(count_free_bootmem());

    totalram_pages += free_all_bootmem();

    --- ./arch/mips64/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/mips64/mm/init.c Sat Nov 10 01:55:30 2001
    @@ -25,6 +25,7 @@
    #ifdef CONFIG_BLK_DEV_INITRD
    #include <linux/blk.h>
    #endif
    +#include <linux/pagemap.h>

    #include <asm/bootinfo.h>
    #include <asm/cachectl.h>
    @@ -396,6 +397,8 @@

    max_mapnr = num_physpages = max_low_pfn;
    high_memory = (void *) __va(max_mapnr << PAGE_SHIFT);
    +
    + page_cache_init(count_free_bootmem());

    totalram_pages += free_all_bootmem();
    totalram_pages -= setup_zero_pages(); /* Setup zeroed pages. */
    --- ./arch/mips64/sgi-ip27/ip27-memory.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/mips64/sgi-ip27/ip27-memory.c Sat Nov 10 02:02:33 2001
    @@ -15,6 +15,7 @@
    #include <linux/mm.h>
    #include <linux/bootmem.h>
    #include <linux/swap.h>
    +#include <linux/pagemap.h>

    #include <asm/page.h>
    #include <asm/bootinfo.h>
    @@ -277,6 +278,11 @@
    num_physpages = numpages; /* memory already sized by szmem */
    max_mapnr = pagenr; /* already found during paging_init */
    high_memory = (void *) __va(max_mapnr << PAGE_SHIFT);
    +
    + tmp = 0;
    + for (nid = 0; nid < numnodes; nid++)
    + tmp += count_free_bootmem_node(NODE_DATA(nid));
    + page_cache_init(tmp);

    for (nid = 0; nid < numnodes; nid++) {

    --- ./arch/parisc/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/parisc/mm/init.c Sat Nov 10 01:57:11 2001
    @@ -17,6 +17,7 @@
    #include <linux/pci.h> /* for hppa_dma_ops and pcxl_dma_ops */
    #include <linux/swap.h>
    #include <linux/unistd.h>
    +#include <linux/pagemap.h>

    #include <asm/pgalloc.h>

    @@ -48,6 +49,8 @@
    {
    max_mapnr = num_physpages = max_low_pfn;
    high_memory = __va(max_low_pfn * PAGE_SIZE);
    +
    + page_cache_init(count_free_bootmem());

    totalram_pages += free_all_bootmem();
    printk("Memory: %luk available\n", totalram_pages << (PAGE_SHIFT-10));
    --- ./arch/cris/mm/init.c.~1~ Sun Oct 21 02:47:53 2001
    +++ ./arch/cris/mm/init.c Sat Nov 10 01:53:10 2001
    @@ -95,6 +95,7 @@
    #include <linux/swap.h>
    #include <linux/smp.h>
    #include <linux/bootmem.h>
    +#include <linux/pagemap.h>

    #include <asm/system.h>
    #include <asm/segment.h>
    @@ -366,6 +367,8 @@

    max_mapnr = num_physpages = max_low_pfn - min_low_pfn;

    + page_cache_init(count_free_bootmem());
    +
    /* this will put all memory onto the freelists */
    totalram_pages = free_all_bootmem();

    --- ./arch/s390x/mm/init.c.~1~ Fri Nov 9 19:08:02 2001
    +++ ./arch/s390x/mm/init.c Sat Nov 10 01:58:14 2001
    @@ -198,6 +198,8 @@
    /* clear the zero-page */
    memset(empty_zero_page, 0, PAGE_SIZE);

    + page_cache_init(count_free_bootmem());
    +
    /* this will put all low memory onto the freelists */
    totalram_pages += free_all_bootmem();

    --- ./include/linux/bootmem.h.~1~ Fri Nov 9 19:35:08 2001
    +++ ./include/linux/bootmem.h Sat Nov 10 02:33:45 2001
    @@ -43,11 +43,13 @@
    #define alloc_bootmem_low_pages(x) \
    __alloc_bootmem((x), PAGE_SIZE, 0)
    extern unsigned long __init free_all_bootmem (void);
    +extern unsigned long __init count_free_bootmem (void);

    extern unsigned long __init init_bootmem_node (pg_data_t *pgdat, unsigned long freepfn, unsigned long startpfn, unsigned long endpfn);
    extern void __init reserve_bootmem_node (pg_data_t *pgdat, unsigned long physaddr, unsigned long size);
    extern void __init free_bootmem_node (pg_data_t *pgdat, unsigned long addr, unsigned long size);
    extern unsigned long __init free_all_bootmem_node (pg_data_t *pgdat);
    +extern unsigned long __init count_free_bootmem_node (pg_data_t *pgdat);
    extern void * __init __alloc_bootmem_node (pg_data_t *pgdat, unsigned long size, unsigned long align, unsigned long goal);
    #define alloc_bootmem_node(pgdat, x) \
    __alloc_bootmem_node((pgdat), (x), SMP_CACHE_BYTES, __pa(MAX_DMA_ADDRESS))
    --- ./init/main.c.~1~ Fri Nov 9 19:08:11 2001
    +++ ./init/main.c Sat Nov 10 04:58:16 2001
    @@ -597,7 +597,6 @@
    proc_caches_init();
    vfs_caches_init(mempages);
    buffer_init(mempages);
    - page_cache_init(mempages);
    #if defined(CONFIG_ARCH_S390)
    ccwcache_init();
    #endif
    --- ./mm/filemap.c.~1~ Fri Nov 9 19:08:11 2001
    +++ ./mm/filemap.c Sat Nov 10 05:15:16 2001
    @@ -24,6 +24,7 @@
    #include <linux/mm.h>
    #include <linux/iobuf.h>
    #include <linux/compiler.h>
    +#include <linux/bootmem.h>

    #include <asm/pgalloc.h>
    #include <asm/uaccess.h>
    @@ -2929,28 +2930,48 @@
    goto unlock;
    }

    +/* This is called from the arch specific mem_init routine.
    + * It is done right before free_all_bootmem (or NUMA equivalent).
    + *
    + * The mempages arg is the number of pages free_all_bootmem is
    + * going to liberate, or a close approximation.
    + *
    + * We have to use bootmem because on huge systems (ie. 16GB ram)
    + * get_free_pages cannot give us a large enough allocation.
    + */
    void __init page_cache_init(unsigned long mempages)
    {
    - unsigned long htable_size, order;
    + unsigned long htable_size, real_size;

    htable_size = mempages;
    htable_size *= sizeof(struct page *);
    - for(order = 0; (PAGE_SIZE << order) < htable_size; order++)
    +
    + for (real_size = 1UL; real_size < htable_size; real_size <<= 1UL)
    ;

    do {
    - unsigned long tmp = (PAGE_SIZE << order) / sizeof(struct page *);
    + unsigned long tmp = (real_size / sizeof(struct page *));
    + unsigned long align;

    page_hash_bits = 0;
    while((tmp >>= 1UL) != 0UL)
    page_hash_bits++;
    +
    + align = real_size;
    + if (align > (4UL * 1024UL * 1024UL))
    + align = (4UL * 1024UL * 1024UL);
    +
    + page_hash_table = __alloc_bootmem(real_size, align,
    + __pa(MAX_DMA_ADDRESS));
    +
    + /* Perhaps the alignment was too strict. */
    + if (page_hash_table == NULL)
    + page_hash_table = alloc_bootmem(real_size);
    + } while (page_hash_table == NULL &&
    + (real_size >>= 1UL) >= PAGE_SIZE);

    - page_hash_table = (struct page **)
    - __get_free_pages(GFP_ATOMIC, order);
    - } while(page_hash_table == NULL && --order > 0);
    -
    - printk("Page-cache hash table entries: %d (order: %ld, %ld bytes)\n",
    - (1 << page_hash_bits), order, (PAGE_SIZE << order));
    + printk("Page-cache hash table entries: %d (%ld bytes)\n",
    + (1 << page_hash_bits), real_size);
    if (!page_hash_table)
    panic("Failed to allocate page hash table\n");
    memset((void *)page_hash_table, 0, PAGE_HASH_SIZE * sizeof(struct page *));
    -
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