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

Nicholas Piggin
2019-06-05T14:49:21Z

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