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mm: Allocate the mm_cpumask (mm->cpu_bitmap[]) dynamically based on nr_cpu_ids

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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>
This commit is contained in:
Rik van Riel
2018-07-16 15:03:31 -04:00
committed by Ingo Molnar
parent 37c45b2354
commit c1a2f7f0c0
4 changed files with 143 additions and 121 deletions
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11
mm/init-mm.c
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@@ -15,6 +15,16 @@
#define INIT_MM_CONTEXT(name)
#endif
/*
* For dynamically allocated mm_structs, there is a dynamically sized cpumask
* at the end of the structure, the size of which depends on the maximum CPU
* number the system can see. That way we allocate only as much memory for
* mm_cpumask() as needed for the hundreds, or thousands of processes that
* a system typically runs.
*
* Since there is only one init_mm in the entire system, keep it simple
* and size this cpu_bitmask to NR_CPUS.
*/
struct mm_struct init_mm = {
.mm_rb = RB_ROOT,
.pgd = swapper_pg_dir,
@@ -25,5 +35,6 @@ struct mm_struct init_mm = {
.arg_lock = __SPIN_LOCK_UNLOCKED(init_mm.arg_lock),
.mmlist = LIST_HEAD_INIT(init_mm.mmlist),
.user_ns = &init_user_ns,
.cpu_bitmap = { [BITS_TO_LONGS(NR_CPUS)] = 0},
INIT_MM_CONTEXT(init_mm)
};