Extend the futex2 interface to be numa aware.
When FUTEX2_NUMA is specified for a futex, the user value is extended
to two words (of the same size). The first is the user value we all
know, the second one will be the node to place this futex on.
struct futex_numa_32 {
u32 val;
u32 node;
};
When node is set to ~0, WAIT will set it to the current node_id such
that WAKE knows where to find it. If userspace corrupts the node value
between WAIT and WAKE, the futex will not be found and no wakeup will
happen.
When FUTEX2_NUMA is not set, the node is simply an extention of the
hash, such that traditional futexes are still interleaved over the
nodes.
This is done to avoid having to have a separate !numa hash-table.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
include/linux/futex.h | 3 +
kernel/futex/core.c | 128 +++++++++++++++++++++++++++++++++++++++---------
kernel/futex/futex.h | 26 +++++++--
kernel/futex/syscalls.c | 2
4 files changed, 127 insertions(+), 32 deletions(-)
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -34,6 +34,7 @@ union futex_key {
u64 i_seq;
unsigned long pgoff;
unsigned int offset;
+ /* unsigned int node; */
} shared;
struct {
union {
@@ -42,11 +43,13 @@ union futex_key {
};
unsigned long address;
unsigned int offset;
+ /* unsigned int node; */
} private;
struct {
u64 ptr;
unsigned long word;
unsigned int offset;
+ unsigned int node; /* NOT hashed! */
} both;
};
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -34,7 +34,8 @@
#include <linux/compat.h>
#include <linux/jhash.h>
#include <linux/pagemap.h>
-#include <linux/memblock.h>
+#include <linux/gfp.h>
+#include <linux/vmalloc.h>
#include <linux/fault-inject.h>
#include <linux/slab.h>
@@ -47,12 +48,14 @@
* reside in the same cacheline.
*/
static struct {
- struct futex_hash_bucket *queues;
unsigned long hashsize;
+ unsigned int hashshift;
+ struct futex_hash_bucket *queues[MAX_NUMNODES];
} __futex_data __read_mostly __aligned(2*sizeof(long));
-#define futex_queues (__futex_data.queues)
-#define futex_hashsize (__futex_data.hashsize)
+#define futex_hashsize (__futex_data.hashsize)
+#define futex_hashshift (__futex_data.hashshift)
+#define futex_queues (__futex_data.queues)
/*
* Fault injections for futexes.
@@ -105,6 +108,26 @@ late_initcall(fail_futex_debugfs);
#endif /* CONFIG_FAIL_FUTEX */
+static int futex_get_value(u32 *val, u32 __user *from, unsigned int flags)
+{
+ switch (futex_size(flags)) {
+ case 1: return __get_user(*val, (u8 __user *)from);
+ case 2: return __get_user(*val, (u16 __user *)from);
+ case 4: return __get_user(*val, (u32 __user *)from);
+ default: BUG();
+ }
+}
+
+static int futex_put_value(u32 val, u32 __user *to, unsigned int flags)
+{
+ switch (futex_size(flags)) {
+ case 1: return __put_user(val, (u8 __user *)to);
+ case 2: return __put_user(val, (u16 __user *)to);
+ case 4: return __put_user(val, (u32 __user *)to);
+ default: BUG();
+ }
+}
+
/**
* futex_hash - Return the hash bucket in the global hash
* @key: Pointer to the futex key for which the hash is calculated
@@ -114,10 +137,29 @@ late_initcall(fail_futex_debugfs);
*/
struct futex_hash_bucket *futex_hash(union futex_key *key)
{
- u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
+ u32 hash = jhash2((u32 *)key,
+ offsetof(typeof(*key), both.offset) / sizeof(u32),
key->both.offset);
+ int node = key->both.node;
- return &futex_queues[hash & (futex_hashsize - 1)];
+ if (node == -1) {
+ /*
+ * In case of !FLAGS_NUMA, use some unused hash bits to pick a
+ * node -- this ensures regular futexes are interleaved across
+ * the nodes and avoids having to allocate multiple
+ * hash-tables.
+ *
+ * NOTE: this isn't perfectly uniform, but it is fast and
+ * handles sparse node masks.
+ */
+ node = (hash >> futex_hashshift) % nr_node_ids;
+ if (!node_possible(node)) {
+ node = find_next_bit_wrap(node_possible_map.bits,
+ nr_node_ids, node);
+ }
+ }
+
+ return &futex_queues[node][hash & (futex_hashsize - 1)];
}
@@ -217,32 +259,55 @@ static u64 get_inode_sequence_number(str
*
* lock_page() might sleep, the caller should not hold a spinlock.
*/
-int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
+int get_futex_key(void __user *uaddr, unsigned int flags, union futex_key *key,
enum futex_access rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
struct page *page, *tail;
struct address_space *mapping;
- int err, ro = 0;
+ int node, err, size, ro = 0;
bool fshared;
fshared = flags & FLAGS_SHARED;
+ size = futex_size(flags);
/*
* The futex address must be "naturally" aligned.
*/
key->both.offset = address % PAGE_SIZE;
- if (unlikely((address % sizeof(u32)) != 0))
+ if (unlikely((address % size) != 0))
return -EINVAL;
address -= key->both.offset;
- if (unlikely(!access_ok(uaddr, sizeof(u32))))
+ if (flags & FLAGS_NUMA)
+ size *= 2;
+
+ if (unlikely(!access_ok(uaddr, size)))
return -EFAULT;
if (unlikely(should_fail_futex(fshared)))
return -EFAULT;
+ key->both.node = -1;
+ if (flags & FLAGS_NUMA) {
+ void __user *naddr = uaddr + size/2;
+
+ if (futex_get_value(&node, naddr, flags))
+ return -EFAULT;
+
+ if (node == -1) {
+ node = numa_node_id();
+ if (futex_put_value(node, naddr, flags))
+ return -EFAULT;
+ }
+
+ if (node >= MAX_NUMNODES || !node_possible(node))
+ return -EINVAL;
+
+ key->both.node = node;
+ }
+
/*
* PROCESS_PRIVATE futexes are fast.
* As the mm cannot disappear under us and the 'key' only needs
@@ -1125,27 +1190,42 @@ void futex_exit_release(struct task_stru
static int __init futex_init(void)
{
- unsigned int futex_shift;
- unsigned long i;
+ unsigned int order, n;
+ unsigned long size, i;
#if CONFIG_BASE_SMALL
futex_hashsize = 16;
#else
- futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
+ futex_hashsize = 256 * num_possible_cpus();
+ futex_hashsize /= num_possible_nodes();
+ futex_hashsize = roundup_pow_of_two(futex_hashsize);
#endif
+ futex_hashshift = ilog2(futex_hashsize);
+ size = sizeof(struct futex_hash_bucket) * futex_hashsize;
+ order = get_order(size);
+
+ for_each_node(n) {
+ struct futex_hash_bucket *table;
+
+ if (order > MAX_ORDER)
+ table = vmalloc_huge_node(size, GFP_KERNEL, n);
+ else
+ table = alloc_pages_exact_nid(n, size, GFP_KERNEL);
+
+ BUG_ON(!table);
+
+ for (i = 0; i < futex_hashsize; i++) {
+ atomic_set(&table[i].waiters, 0);
+ spin_lock_init(&table[i].lock);
+ plist_head_init(&table[i].chain);
+ }
- futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
- futex_hashsize, 0,
- futex_hashsize < 256 ? HASH_SMALL : 0,
- &futex_shift, NULL,
- futex_hashsize, futex_hashsize);
- futex_hashsize = 1UL << futex_shift;
-
- for (i = 0; i < futex_hashsize; i++) {
- atomic_set(&futex_queues[i].waiters, 0);
- plist_head_init(&futex_queues[i].chain);
- spin_lock_init(&futex_queues[i].lock);
+ futex_queues[n] = table;
}
+ pr_info("futex hash table, %d nodes, %ld entries (order: %d, %lu bytes)\n",
+ num_possible_nodes(),
+ futex_hashsize, order,
+ sizeof(struct futex_hash_bucket) * futex_hashsize);
return 0;
}
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -65,6 +65,12 @@ static inline unsigned int futex2_to_fla
return flags;
}
+static inline unsigned int futex_size(unsigned int flags)
+{
+ unsigned int size = flags & FLAGS_SIZE_MASK;
+ return 1 << size; /* {0,1,2,3} -> {1,2,4,8} */
+}
+
static inline bool futex_flags_valid(unsigned int flags)
{
/* Only 64bit futexes for 64bit code */
@@ -77,13 +83,19 @@ static inline bool futex_flags_valid(uns
if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32)
return false;
- return true;
-}
+ /*
+ * Must be able to represent both NUMA_NO_NODE and every valid nodeid
+ * in a futex word.
+ */
+ if (flags & FLAGS_NUMA) {
+ int bits = 8 * futex_size(flags);
+ u64 max = ~0ULL;
+ max >>= 64 - bits;
+ if (nr_node_ids >= max)
+ return false;
+ }
-static inline unsigned int futex_size(unsigned int flags)
-{
- unsigned int size = flags & FLAGS_SIZE_MASK;
- return 1 << size; /* {0,1,2,3} -> {1,2,4,8} */
+ return true;
}
static inline bool futex_validate_input(unsigned int flags, u64 val)
@@ -182,7 +194,7 @@ enum futex_access {
FUTEX_WRITE
};
-extern int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
+extern int get_futex_key(void __user *uaddr, unsigned int flags, union futex_key *key,
enum futex_access rw);
extern struct hrtimer_sleeper *
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -179,7 +179,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uad
return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
}
-#define FUTEX2_MASK (FUTEX2_64 | FUTEX2_PRIVATE)
+#define FUTEX2_MASK (FUTEX2_64 | FUTEX2_NUMA | FUTEX2_PRIVATE)
/**
* futex_parse_waitv - Parse a waitv array from userspace
On Fri, Jul 21, 2023 at 12:22:48PM +0200, Peter Zijlstra wrote:
> @@ -217,32 +259,55 @@ static u64 get_inode_sequence_number(str
> *
> * lock_page() might sleep, the caller should not hold a spinlock.
> */
> -int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
> +int get_futex_key(void __user *uaddr, unsigned int flags, union futex_key *key,
> enum futex_access rw)
> {
> unsigned long address = (unsigned long)uaddr;
> struct mm_struct *mm = current->mm;
> struct page *page, *tail;
> struct address_space *mapping;
> + int node, err, size, ro = 0;
> bool fshared;
>
> fshared = flags & FLAGS_SHARED;
> + size = futex_size(flags);
>
> /*
> * The futex address must be "naturally" aligned.
> */
> key->both.offset = address % PAGE_SIZE;
> + if (unlikely((address % size) != 0))
> return -EINVAL;
This enforces u32 alignment for:
struct futex_numa_32 {
u32 val;
u32 node;
};
Or do we want to enfore u64 alignment for that?
> address -= key->both.offset;
>
> + if (flags & FLAGS_NUMA)
> + size *= 2;
> +
> + if (unlikely(!access_ok(uaddr, size)))
> return -EFAULT;
On Fri, Jul 21 2023 at 12:22, Peter Zijlstra wrote:
> struct futex_hash_bucket *futex_hash(union futex_key *key)
> {
> - u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
> + u32 hash = jhash2((u32 *)key,
> + offsetof(typeof(*key), both.offset) / sizeof(u32),
> key->both.offset);
> + int node = key->both.node;
>
> - return &futex_queues[hash & (futex_hashsize - 1)];
> + if (node == -1) {
> + /*
> + * In case of !FLAGS_NUMA, use some unused hash bits to pick a
> + * node -- this ensures regular futexes are interleaved across
> + * the nodes and avoids having to allocate multiple
> + * hash-tables.
> + *
> + * NOTE: this isn't perfectly uniform, but it is fast and
> + * handles sparse node masks.
> + */
> + node = (hash >> futex_hashshift) % nr_node_ids;
Is nr_node_ids guaranteed to be stable after init? It's marked
__read_mostly, but not __ro_after_init.
> + if (!node_possible(node)) {
> + node = find_next_bit_wrap(node_possible_map.bits,
> + nr_node_ids, node);
> + }
> + }
> +
> + return &futex_queues[node][hash & (futex_hashsize - 1)];
> }
> fshared = flags & FLAGS_SHARED;
> + size = futex_size(flags);
>
> /*
> * The futex address must be "naturally" aligned.
> */
> key->both.offset = address % PAGE_SIZE;
> - if (unlikely((address % sizeof(u32)) != 0))
> + if (unlikely((address % size) != 0))
> return -EINVAL;
Hmm. Shouldn't that have changed with the allowance of the 1 and 2 byte
futexes?
> address -= key->both.offset;
>
> - if (unlikely(!access_ok(uaddr, sizeof(u32))))
> + if (flags & FLAGS_NUMA)
> + size *= 2;
> +
> + if (unlikely(!access_ok(uaddr, size)))
> return -EFAULT;
>
> if (unlikely(should_fail_futex(fshared)))
> return -EFAULT;
>
> + key->both.node = -1;
Please put this into an else path.
> + if (flags & FLAGS_NUMA) {
> + void __user *naddr = uaddr + size/2;
size / 2;
> +
> + if (futex_get_value(&node, naddr, flags))
> + return -EFAULT;
> +
> + if (node == -1) {
> + node = numa_node_id();
> + if (futex_put_value(node, naddr, flags))
> + return -EFAULT;
> + }
> +
> + if (node >= MAX_NUMNODES || !node_possible(node))
> + return -EINVAL;
That's clearly an else path too. No point in checking whether
numa_node_id() is valid.
> + key->both.node = node;
> + }
>
> +static inline unsigned int futex_size(unsigned int flags)
> +{
> + unsigned int size = flags & FLAGS_SIZE_MASK;
> + return 1 << size; /* {0,1,2,3} -> {1,2,4,8} */
> +}
> +
> static inline bool futex_flags_valid(unsigned int flags)
> {
> /* Only 64bit futexes for 64bit code */
> @@ -77,13 +83,19 @@ static inline bool futex_flags_valid(uns
> if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32)
> return false;
>
> - return true;
> -}
> + /*
> + * Must be able to represent both NUMA_NO_NODE and every valid nodeid
> + * in a futex word.
> + */
> + if (flags & FLAGS_NUMA) {
> + int bits = 8 * futex_size(flags);
> + u64 max = ~0ULL;
> + max >>= 64 - bits;
Your newline key is broken, right?
> + if (nr_node_ids >= max)
> + return false;
> + }
Thanks,
tglx
On Mon, Jul 31, 2023 at 07:36:21PM +0200, Thomas Gleixner wrote:
> On Fri, Jul 21 2023 at 12:22, Peter Zijlstra wrote:
> > struct futex_hash_bucket *futex_hash(union futex_key *key)
> > {
> > - u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
> > + u32 hash = jhash2((u32 *)key,
> > + offsetof(typeof(*key), both.offset) / sizeof(u32),
> > key->both.offset);
> > + int node = key->both.node;
> >
> > - return &futex_queues[hash & (futex_hashsize - 1)];
> > + if (node == -1) {
> > + /*
> > + * In case of !FLAGS_NUMA, use some unused hash bits to pick a
> > + * node -- this ensures regular futexes are interleaved across
> > + * the nodes and avoids having to allocate multiple
> > + * hash-tables.
> > + *
> > + * NOTE: this isn't perfectly uniform, but it is fast and
> > + * handles sparse node masks.
> > + */
> > + node = (hash >> futex_hashshift) % nr_node_ids;
>
> Is nr_node_ids guaranteed to be stable after init? It's marked
> __read_mostly, but not __ro_after_init.
AFAICT it is only ever written to in setup_nr_node_ids() and that is all
__init code. So I'm thinking this could/should indeed be
__ro_after_init. Esp. so since it is an exported variable.
Mike?
> > + if (!node_possible(node)) {
> > + node = find_next_bit_wrap(node_possible_map.bits,
> > + nr_node_ids, node);
> > + }
> > + }
> > +
> > + return &futex_queues[node][hash & (futex_hashsize - 1)];
> > }
> > fshared = flags & FLAGS_SHARED;
> > + size = futex_size(flags);
> >
> > /*
> > * The futex address must be "naturally" aligned.
> > */
> > key->both.offset = address % PAGE_SIZE;
> > - if (unlikely((address % sizeof(u32)) != 0))
> > + if (unlikely((address % size) != 0))
> > return -EINVAL;
>
> Hmm. Shouldn't that have changed with the allowance of the 1 and 2 byte
> futexes?
That patches comes after this.. :-)
But I do have an open question here; do we want FUTEX2_NUMA futexes
aligned at futex_size or double that? That is, what do we want the
alignment of:
struct futex_numa_32 {
u32 val;
u32 node;
};
to be? Having that u64 aligned will guarantee these two values end up in
the same page, having them u32 aligned (as per this patch) allows for
them to be split.
The current paths don't care, we don't hold locks, but perhaps it makes
sense to be conservative.
> > address -= key->both.offset;
> >
> > - if (unlikely(!access_ok(uaddr, sizeof(u32))))
> > + if (flags & FLAGS_NUMA)
> > + size *= 2;
> > +
> > + if (unlikely(!access_ok(uaddr, size)))
> > return -EFAULT;
> >
> > if (unlikely(should_fail_futex(fshared)))
> > return -EFAULT;
> >
> > + key->both.node = -1;
>
> Please put this into an else path.
Can do, but I figured the compiler could figure it out through dead
store elimitation or somesuch pass.
> > + if (flags & FLAGS_NUMA) {
> > + void __user *naddr = uaddr + size/2;
>
> size / 2;
>
> > +
> > + if (futex_get_value(&node, naddr, flags))
> > + return -EFAULT;
> > +
> > + if (node == -1) {
> > + node = numa_node_id();
> > + if (futex_put_value(node, naddr, flags))
> > + return -EFAULT;
> > + }
> > +
> > + if (node >= MAX_NUMNODES || !node_possible(node))
> > + return -EINVAL;
>
> That's clearly an else path too. No point in checking whether
> numa_node_id() is valid.
No, this also checks if the value we read from userspace is valid.
Only when the value we read from userspace is -1 do we set
numa_node_id(), otherwise we take the value as read, which then must be
a valid value.
> > + key->both.node = node;
> > + }
> >
> > +static inline unsigned int futex_size(unsigned int flags)
> > +{
> > + unsigned int size = flags & FLAGS_SIZE_MASK;
> > + return 1 << size; /* {0,1,2,3} -> {1,2,4,8} */
> > +}
> > +
> > static inline bool futex_flags_valid(unsigned int flags)
> > {
> > /* Only 64bit futexes for 64bit code */
> > @@ -77,13 +83,19 @@ static inline bool futex_flags_valid(uns
> > if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32)
> > return false;
> >
> > - return true;
> > -}
> > + /*
> > + * Must be able to represent both NUMA_NO_NODE and every valid nodeid
> > + * in a futex word.
> > + */
> > + if (flags & FLAGS_NUMA) {
> > + int bits = 8 * futex_size(flags);
> > + u64 max = ~0ULL;
> > + max >>= 64 - bits;
> Your newline key is broken, right?
Yes :-)
> > + if (nr_node_ids >= max)
> > + return false;
> > + }
On Mon, Jul 31 2023 at 20:03, Peter Zijlstra wrote:
> On Mon, Jul 31, 2023 at 07:36:21PM +0200, Thomas Gleixner wrote:
>> Hmm. Shouldn't that have changed with the allowance of the 1 and 2 byte
>> futexes?
>
> That patches comes after this.. :-)
Futexes are really cursed :)
> But I do have an open question here; do we want FUTEX2_NUMA futexes
> aligned at futex_size or double that? That is, what do we want the
> alignment of:
>
> struct futex_numa_32 {
> u32 val;
> u32 node;
> };
>
> to be? Having that u64 aligned will guarantee these two values end up in
> the same page, having them u32 aligned (as per this patch) allows for
> them to be split.
Same page and same cacheline.
> The current paths don't care, we don't hold locks, but perhaps it makes
> sense to be conservative.
I think it makes sense.
>> > address -= key->both.offset;
>> >
>> > - if (unlikely(!access_ok(uaddr, sizeof(u32))))
>> > + if (flags & FLAGS_NUMA)
>> > + size *= 2;
>> > +
>> > + if (unlikely(!access_ok(uaddr, size)))
>> > return -EFAULT;
>> >
>> > if (unlikely(should_fail_futex(fshared)))
>> > return -EFAULT;
>> >
>> > + key->both.node = -1;
>>
>> Please put this into an else path.
>
> Can do, but I figured the compiler could figure it out through dead
> store elimitation or somesuch pass.
Sure, but taste disagrees and it simply makes the code more obvious.
>> > + if (flags & FLAGS_NUMA) {
>> > + void __user *naddr = uaddr + size/2;
>>
>> size / 2;
>>
>> > +
>> > + if (futex_get_value(&node, naddr, flags))
>> > + return -EFAULT;
>> > +
>> > + if (node == -1) {
>> > + node = numa_node_id();
>> > + if (futex_put_value(node, naddr, flags))
>> > + return -EFAULT;
>> > + }
>> > +
>> > + if (node >= MAX_NUMNODES || !node_possible(node))
>> > + return -EINVAL;
>>
>> That's clearly an else path too. No point in checking whether
>> numa_node_id() is valid.
>
> No, this also checks if the value we read from userspace is valid.
>
> Only when the value we read from userspace is -1 do we set
> numa_node_id(), otherwise we take the value as read, which then must be
> a valid value.
Right, but:
if (node == -1) {
node = numa_node_id();
if (futex_put_value(node, naddr, flags))
return -EFAULT;
} else if (node >= MAX_NUMNODES || !node_possible(node)) {
return -EINVAL;
}
makes it clear that the path where @node read from user space is != -1
needs to be validated, while your version checks the result of
node = numa_node_id();
too, which does not make sense to me. Yes, it works, but ...
Thanks,
tglx
On Mon, 31 Jul 2023, Peter Zijlstra wrote:
>> Is nr_node_ids guaranteed to be stable after init? It's marked
>> __read_mostly, but not __ro_after_init.
>
> AFAICT it is only ever written to in setup_nr_node_ids() and that is all
> __init code. So I'm thinking this could/should indeed be
> __ro_after_init. Esp. so since it is an exported variable.
>
> Mike?
Its stable and lots of other components depend on it like f.e. the size of
cpumasks.
On Wed, Jun 12, 2024 at 10:23:00AM -0700, Christoph Lameter (Ampere) wrote:
> On Fri, 21 Jul 2023, Peter Zijlstra wrote:
>
> > Extend the futex2 interface to be numa aware.
>
> Sorry to be chiming in that late but it seems that this is useful to
> mitigate NUMA issues also for our platform.
I read this like: I tested it and it works for me. Is that a correct
reading of your statement?
If so, I'll look at bumping this on the priority list and I'll look at
the placement suggestion you had when I respin the patches.
Thanks!
On Fri, 21 Jul 2023, Peter Zijlstra wrote:
> Extend the futex2 interface to be numa aware.
Sorry to be chiming in that late but it seems that this is useful to
mitigate NUMA issues also for our platform.
> When FUTEX2_NUMA is not set, the node is simply an extention of the
> hash, such that traditional futexes are still interleaved over the
> nodes.
Could we follow NUMA policies like with other metadata allocations during
systen call processing? If there is no NUMA task policy then the futex
should be placed on the local NUMA node.
That way the placement of the futex can be controlled by the tasks memory
policy. We could skip the FUTEX2_NUMA option.
> @@ -114,10 +137,29 @@ late_initcall(fail_futex_debugfs);
> */
> struct futex_hash_bucket *futex_hash(union futex_key *key)
> {
> - u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
> + u32 hash = jhash2((u32 *)key,
> + offsetof(typeof(*key), both.offset) / sizeof(u32),
> key->both.offset);
> + int node = key->both.node;
>
> - return &futex_queues[hash & (futex_hashsize - 1)];
> + if (node == -1) {
> + /*
> + * In case of !FLAGS_NUMA, use some unused hash bits to pick a
> + * node -- this ensures regular futexes are interleaved across
> + * the nodes and avoids having to allocate multiple
> + * hash-tables.
> + *
> + * NOTE: this isn't perfectly uniform, but it is fast and
> + * handles sparse node masks.
> + */
> + node = (hash >> futex_hashshift) % nr_node_ids;
> + if (!node_possible(node)) {
> + node = find_next_bit_wrap(node_possible_map.bits,
> + nr_node_ids, node);
> + }
Use memory allocation policies here instead?