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    Subject[PATCH 1/2] mm/large system hash: use vmalloc for size > MAX_ORDER when !hashdist
    Date
    The kernel currently clamps large system hashes to MAX_ORDER when
    hashdist is not set, which is rather arbitrary.

    vmalloc space is limited on 32-bit machines, but this shouldn't
    result in much more used because of small physical memory limiting
    system hash sizes.

    Include "vmalloc" or "linear" in the kernel log message.

    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
    ---

    This is a better solution than the previous one for the case of !NUMA
    systems running on CONFIG_NUMA kernels, we can clear the default
    hashdist early and have everything allocated out of the linear map.

    The hugepage vmap series I will post later, but it's quite
    independent from this improvement.

    mm/page_alloc.c | 16 +++++++++-------
    1 file changed, 9 insertions(+), 7 deletions(-)

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index d66bc8abe0af..15f46be7d210 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -7966,6 +7966,7 @@ void *__init alloc_large_system_hash(const char *tablename,
    unsigned long log2qty, size;
    void *table = NULL;
    gfp_t gfp_flags;
    + bool virt;

    /* allow the kernel cmdline to have a say */
    if (!numentries) {
    @@ -8022,6 +8023,7 @@ void *__init alloc_large_system_hash(const char *tablename,

    gfp_flags = (flags & HASH_ZERO) ? GFP_ATOMIC | __GFP_ZERO : GFP_ATOMIC;
    do {
    + virt = false;
    size = bucketsize << log2qty;
    if (flags & HASH_EARLY) {
    if (flags & HASH_ZERO)
    @@ -8029,26 +8031,26 @@ void *__init alloc_large_system_hash(const char *tablename,
    else
    table = memblock_alloc_raw(size,
    SMP_CACHE_BYTES);
    - } else if (hashdist) {
    + } else if (get_order(size) >= MAX_ORDER || hashdist) {
    table = __vmalloc(size, gfp_flags, PAGE_KERNEL);
    + virt = true;
    } else {
    /*
    * If bucketsize is not a power-of-two, we may free
    * some pages at the end of hash table which
    * alloc_pages_exact() automatically does
    */
    - if (get_order(size) < MAX_ORDER) {
    - table = alloc_pages_exact(size, gfp_flags);
    - kmemleak_alloc(table, size, 1, gfp_flags);
    - }
    + table = alloc_pages_exact(size, gfp_flags);
    + kmemleak_alloc(table, size, 1, gfp_flags);
    }
    } while (!table && size > PAGE_SIZE && --log2qty);

    if (!table)
    panic("Failed to allocate %s hash table\n", tablename);

    - pr_info("%s hash table entries: %ld (order: %d, %lu bytes)\n",
    - tablename, 1UL << log2qty, ilog2(size) - PAGE_SHIFT, size);
    + pr_info("%s hash table entries: %ld (order: %d, %lu bytes, %s)\n",
    + tablename, 1UL << log2qty, ilog2(size) - PAGE_SHIFT, size,
    + virt ? "vmalloc" : "linear");

    if (_hash_shift)
    *_hash_shift = log2qty;
    --
    2.20.1
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