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

Andrew Morton
2019-06-05T21:22:11Z

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?