Re: [PATCH 1/2] mm/large system hash: use vmalloc for size > MAX_ORDER when !hashdist

Nicholas Piggin
2019-06-06T02:28:12Z

Andrew Morton's on June 6, 2019 7:22 am:
> On Thu, 6 Jun 2019 00:48:13 +1000 Nicholas Piggin <npiggin@gmail.com> wrote:
>
>> 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.
>>
>> ...
>>
>> --- 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");
>
> Could remove `bool virt' and use is_vmalloc_addr() in the printk?
>

It can run before mem_init() and it looks like some archs set
VMALLOC_START/END (high_memory) there (e.g., x86-32, ppc32).

Thanks,
Nick