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authorRik van Riel <riel@surriel.com>2018-07-16 15:03:31 -0400
committerIngo Molnar <mingo@kernel.org>2018-07-17 09:35:30 +0200
commitc1a2f7f0c06454387c2cd7b93ff1491c715a8c69 (patch)
treef3b3cce7e45b2bab54681b23a3947a445ae38a37 /kernel/fork.c
parent37c45b2354cb2270f246679bedd8bf798cca351c (diff)
downloadlwn-c1a2f7f0c06454387c2cd7b93ff1491c715a8c69.tar.gz
lwn-c1a2f7f0c06454387c2cd7b93ff1491c715a8c69.zip
mm: Allocate the mm_cpumask (mm->cpu_bitmap[]) dynamically based on nr_cpu_ids
The mm_struct always contains a cpumask bitmap, regardless of CONFIG_CPUMASK_OFFSTACK. That means the first step can be to simplify things, and simply have one bitmask at the end of the mm_struct for the mm_cpumask. This does necessitate moving everything else in mm_struct into an anonymous sub-structure, which can be randomized when struct randomization is enabled. The second step is to determine the correct size for the mm_struct slab object from the size of the mm_struct (excluding the CPU bitmap) and the size the cpumask. For init_mm we can simply allocate the maximum size this kernel is compiled for, since we only have one init_mm in the system, anyway. Pointer magic by Mike Galbraith, to evade -Wstringop-overflow getting confused by the dynamically sized array. Tested-by: Song Liu <songliubraving@fb.com> Signed-off-by: Rik van Riel <riel@surriel.com> Signed-off-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Rik van Riel <riel@surriel.com> Acked-by: Dave Hansen <dave.hansen@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@fb.com Cc: luto@kernel.org Link: http://lkml.kernel.org/r/20180716190337.26133-2-riel@surriel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c15
1 files changed, 9 insertions, 6 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 9440d61b925c..5b64c1b8461e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2253,6 +2253,8 @@ static void sighand_ctor(void *data)
void __init proc_caches_init(void)
{
+ unsigned int mm_size;
+
sighand_cachep = kmem_cache_create("sighand_cache",
sizeof(struct sighand_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
@@ -2269,15 +2271,16 @@ void __init proc_caches_init(void)
sizeof(struct fs_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
NULL);
+
/*
- * FIXME! The "sizeof(struct mm_struct)" currently includes the
- * whole struct cpumask for the OFFSTACK case. We could change
- * this to *only* allocate as much of it as required by the
- * maximum number of CPU's we can ever have. The cpumask_allocation
- * is at the end of the structure, exactly for that reason.
+ * The mm_cpumask is located at the end of mm_struct, and is
+ * dynamically sized based on the maximum CPU number this system
+ * can have, taking hotplug into account (nr_cpu_ids).
*/
+ mm_size = sizeof(struct mm_struct) + cpumask_size();
+
mm_cachep = kmem_cache_create_usercopy("mm_struct",
- sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
+ mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
offsetof(struct mm_struct, saved_auxv),
sizeof_field(struct mm_struct, saved_auxv),