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mm, mempolicy: remove per-process flag

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PF_MEMPOLICY is an unnecessary optimization for CONFIG_SLAB users.
There's no significant performance degradation to checking
current->mempolicy rather than current->flags & PF_MEMPOLICY in the
allocation path, especially since this is considered unlikely().

Running TCP_RR with netperf-2.4.5 through localhost on 16 cpu machine with
64GB of memory and without a mempolicy:

	threads		before		after
	16		1249409		1244487
	32		1281786		1246783
	48		1239175		1239138
	64		1244642		1241841
	80		1244346		1248918
	96		1266436		1254316
	112		1307398		1312135
	128		1327607		1326502

Per-process flags are a scarce resource so we should free them up whenever
possible and make them available.  We'll be using it shortly for memcg oom
reserves.

Signed-off-by: David Rientjes <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Jianguo Wu <[email protected]>
Cc: Tim Hockin <[email protected]>
Cc: Christoph Lameter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
David Rientjes 2014-04-07 15:37:30 -07:00 • committed by Linus Torvalds
commit f0432d1596
5 changed files with 2 additions and 36 deletions
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31
mm/mempolicy.c
View file

@ -795,36 +795,6 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
return err;
}
/*
* Update task->flags PF_MEMPOLICY bit: set iff non-default
* mempolicy. Allows more rapid checking of this (combined perhaps
* with other PF_* flag bits) on memory allocation hot code paths.
*
* If called from outside this file, the task 'p' should -only- be
* a newly forked child not yet visible on the task list, because
* manipulating the task flags of a visible task is not safe.
*
* The above limitation is why this routine has the funny name
* mpol_fix_fork_child_flag().
*
* It is also safe to call this with a task pointer of current,
* which the static wrapper mpol_set_task_struct_flag() does,
* for use within this file.
*/
void mpol_fix_fork_child_flag(struct task_struct *p)
{
if (p->mempolicy)
p->flags |= PF_MEMPOLICY;
else
p->flags &= ~PF_MEMPOLICY;
}
static void mpol_set_task_struct_flag(void)
{
mpol_fix_fork_child_flag(current);
}
/* Set the process memory policy */
static long do_set_mempolicy(unsigned short mode, unsigned short flags,
nodemask_t *nodes)
@ -861,7 +831,6 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
}
old = current->mempolicy;
current->mempolicy = new;
mpol_set_task_struct_flag();
if (new && new->mode == MPOL_INTERLEAVE &&
nodes_weight(new->v.nodes))
current->il_next = first_node(new->v.nodes);

4
mm/slab.c
View file

@ -3027,7 +3027,7 @@ out:
#ifdef CONFIG_NUMA
/*
* Try allocating on another node if PF_SPREAD_SLAB|PF_MEMPOLICY.
* Try allocating on another node if PF_SPREAD_SLAB is a mempolicy is set.
*
* If we are in_interrupt, then process context, including cpusets and
* mempolicy, may not apply and should not be used for allocation policy.
@ -3259,7 +3259,7 @@ __do_cache_alloc(struct kmem_cache *cache, gfp_t flags)
{
void *objp;
if (unlikely(current->flags & (PF_SPREAD_SLAB | PF_MEMPOLICY))) {
if (current->mempolicy || unlikely(current->flags & PF_SPREAD_SLAB)) {
objp = alternate_node_alloc(cache, flags);
if (objp)
goto out;