From: Vlastimil Babka vbabka@suse.cz
mainline inclusion from mainline-v6.0-rc1 commit f9987921cb541b1187a648141a9048547ea89ffb category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9GSSR
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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As Linus explained [1], setting the stackdepot hash table size as a config option is suboptimal, especially as stackdepot becomes a dependency of less "expert" subsystems than initially (e.g. DRM, networking, SLUB_DEBUG):
: (a) it introduces a new compile-time question that isn't sane to ask : a regular user, but is now exposed to regular users.
: (b) this by default uses 1MB of memory for a feature that didn't in : the past, so now if you have small machines you need to make sure you : make a special kernel config for them.
Ideally we would employ rhashtable for fully automatic resizing, which should be feasible for many of the new users, but problematic for the original users with restricted context that call __stack_depot_save() with can_alloc == false, i.e. KASAN.
However we can easily remove the config option and scale the hash table automatically with system memory. The STACK_HASH_MASK constant becomes stack_hash_mask variable and is used only in one mask operation, so the overhead should be negligible to none. For early allocation we can employ the existing alloc_large_system_hash() function and perform similar scaling for the late allocation.
The existing limits of the config option (between 4k and 1M buckets) are preserved, and scaling factor is set to one bucket per 16kB memory so on 64bit the max 1M buckets (8MB memory) is achieved with 16GB system, while a 1GB system will use 512kB.
Because KASAN is reported to need the maximum number of buckets even with smaller amounts of memory [2], set it as such when kasan_enabled().
If needed, the automatic scaling could be complemented with a boot-time kernel parameter, but it feels pointless to add it without a specific use case.
[1] https://lore.kernel.org/all/CAHk-=wjC5nS+fnf6EzRD9yQRJApAhxx7gRB87ZV+pAWo9oV... [2] https://lore.kernel.org/all/CACT4Y+Y4GZfXOru2z5tFPzFdaSUd+GFc6KVL=bsa0+1m197...
Link: https://lkml.kernel.org/r/20220620150249.16814-1-vbabka@suse.cz Signed-off-by: Vlastimil Babka vbabka@suse.cz Reported-by: Linus Torvalds torvalds@linux-foundation.org Acked-by: Dmitry Vyukov dvyukov@google.com Cc: Marco Elver elver@google.com Cc: Alexander Potapenko glider@google.com Cc: Andrey Konovalov andreyknvl@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org
Conflicts: lib/Kconfig lib/stackdepot.c [lib/stackdepot.c needs to call kasan_enabled() that hasn't been merged, call IS_ENABLED(CONFIG_KASAN) directly. other conflicts are context conflicts] Signed-off-by: Jinjiang Tu tujinjiang@huawei.com --- lib/Kconfig | 9 -------- lib/stackdepot.c | 59 ++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 49 insertions(+), 19 deletions(-)
diff --git a/lib/Kconfig b/lib/Kconfig index 06a796a94828..497304f1647c 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -664,15 +664,6 @@ config STACKDEPOT bool select STACKTRACE
-config STACK_HASH_ORDER - int "stack depot hash size (12 => 4KB, 20 => 1024KB)" - range 12 20 - default 20 - depends on STACKDEPOT - help - Select the hash size as a power of 2 for the stackdepot hash table. - Choose a lower value to reduce the memory impact. - config STACKDEPOT_ALWAYS_INIT bool select STACKDEPOT diff --git a/lib/stackdepot.c b/lib/stackdepot.c index e3275f07076c..2f73c861e81c 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -32,6 +32,7 @@ #include <linux/string.h> #include <linux/types.h> #include <linux/memblock.h> +extern unsigned long nr_free_buffer_pages(void);
#define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
@@ -146,10 +147,16 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size, return stack; }
-#define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER) -#define STACK_HASH_MASK (STACK_HASH_SIZE - 1) +/* one hash table bucket entry per 16kB of memory */ +#define STACK_HASH_SCALE 14 +/* limited between 4k and 1M buckets */ +#define STACK_HASH_ORDER_MIN 12 +#define STACK_HASH_ORDER_MAX 20 #define STACK_HASH_SEED 0x9747b28c
+static unsigned int stack_hash_order; +static unsigned int stack_hash_mask; + static bool stack_depot_disable; static struct stack_record **stack_table;
@@ -176,7 +183,7 @@ void __init stack_depot_want_early_init(void)
int __init stack_depot_early_init(void) { - size_t size; + unsigned long entries = 0;
/* This is supposed to be called only once, from mm_init() */ if (WARN_ON(__stack_depot_early_init_passed)) @@ -184,13 +191,23 @@ int __init stack_depot_early_init(void)
__stack_depot_early_init_passed = true;
+ if (IS_ENABLED(CONFIG_KASAN) && !stack_hash_order) + stack_hash_order = STACK_HASH_ORDER_MAX; + if (!__stack_depot_want_early_init || stack_depot_disable) return 0;
- size = (STACK_HASH_SIZE * sizeof(struct stack_record *)); - pr_info("Stack Depot early init allocating hash table with memblock_alloc, %zu bytes\n", - size); - stack_table = memblock_alloc(size, SMP_CACHE_BYTES); + if (stack_hash_order) + entries = 1UL << stack_hash_order; + stack_table = alloc_large_system_hash("stackdepot", + sizeof(struct stack_record *), + entries, + STACK_HASH_SCALE, + HASH_EARLY | HASH_ZERO, + NULL, + &stack_hash_mask, + 1UL << STACK_HASH_ORDER_MIN, + 1UL << STACK_HASH_ORDER_MAX);
if (!stack_table) { pr_err("Stack Depot hash table allocation failed, disabling\n"); @@ -208,13 +225,35 @@ int stack_depot_init(void)
mutex_lock(&stack_depot_init_mutex); if (!stack_depot_disable && !stack_table) { - pr_info("Stack Depot allocating hash table with kvcalloc\n"); - stack_table = kvcalloc(STACK_HASH_SIZE, sizeof(struct stack_record *), GFP_KERNEL); + unsigned long entries; + int scale = STACK_HASH_SCALE; + + if (stack_hash_order) { + entries = 1UL << stack_hash_order; + } else { + entries = nr_free_buffer_pages(); + entries = roundup_pow_of_two(entries); + + if (scale > PAGE_SHIFT) + entries >>= (scale - PAGE_SHIFT); + else + entries <<= (PAGE_SHIFT - scale); + } + + if (entries < 1UL << STACK_HASH_ORDER_MIN) + entries = 1UL << STACK_HASH_ORDER_MIN; + if (entries > 1UL << STACK_HASH_ORDER_MAX) + entries = 1UL << STACK_HASH_ORDER_MAX; + + pr_info("Stack Depot allocating hash table of %lu entries with kvcalloc\n", + entries); + stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL); if (!stack_table) { pr_err("Stack Depot hash table allocation failed, disabling\n"); stack_depot_disable = true; ret = -ENOMEM; } + stack_hash_mask = entries - 1; } mutex_unlock(&stack_depot_init_mutex); return ret; @@ -317,7 +356,7 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries, goto fast_exit;
hash = hash_stack(entries, nr_entries); - bucket = &stack_table[hash & STACK_HASH_MASK]; + bucket = &stack_table[hash & stack_hash_mask];
/* * Fast path: look the stack trace up without locking.