linux-kernel - [PATCH 1/2] mm/large system hash: use vmalloc for size > MAX

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Date:   Thu,  6 Jun 2019 00:48:13 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     linux-mm@...ck.org
Cc:     Nicholas Piggin <npiggin@...il.com>, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 1/2] mm/large system hash: use vmalloc for size > MAX_ORDER when !hashdist

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@...il.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