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Date: Thu, 30 Jul 2009 09:06:21 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: kosaki.motohiro@...fujitsu.com, miaox@...fujitsu.com,
mingo@...e.hu, a.p.zijlstra@...llo.nl, cl@...ux-foundation.org,
menage@...gle.com, nickpiggin@...oo.com.au, y-goto@...fujitsu.com,
penberg@...helsinki.fi, rientjes@...gle.com,
lee.schermerhorn@...com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX] set_mempolicy(MPOL_INTERLEAV) N_HIGH_MEMORY aware
On Wed, 29 Jul 2009 13:16:00 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue, 28 Jul 2009 16:18:13 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
> > tested on x86-64/fake NUMA and ia64/NUMA.
> > (That ia64 is a host which orignal bug report used.)
>
> There's no description here of this bug.
>
> Does this patch actually fix a bug? Seems not. Confusing.
>
yes. fix a bug. maybe my description is not good.
The bug itself is orignally reporeted here:
http://marc.info/?l=linux-kernel&m=124765131625716&w=2
Ok, let me explain what happened.
At first, init_task's mems_allowed is initialized as this.
init_task->mems_allowed == node_state[N_POSSIBLE]
And cpuset's top_cpuset mask is initialized as this
top_cpuset->mems_allowed = node_state[N_HIGH_MEMORY]
Before 2.6.29:
policy's mems_allowed is initialized as this.
1. update tasks->mems_allowed by its cpuset->mems_allowed.
2. policy->mems_allowed = nodes_and(tasks->mems_allowed, user's mask)
Updating task's mems_allowed in reference to top_cpuset's one.
cpuset's mems_allowed is aware of N_HIGH_MEMORY, always.
In 2.6.30: After commit=58568d2a8215cb6f55caf2332017d7bdff954e1c
policy's mems_allowed is initialized as this.
1. policy->mems_allowd = nodes_and(task->mems_allowed, user's mask)
Here, if task is in top_cpuset, task->mems_allowed is not updated from init's
one. Assume user excutes command as
#numactrl --interleave=all ,....
policy->mems_allowd = nodes_and(N_POSSIBLE, ALL_SET_MASK)
Then, policy's mems_allowd can includes a possible node, which has no pgdat.
MPOL's INTERLEAVE just scans nodemask of task->mems_allowd and access this
directly.
NODE_DATA(nid)->zonelist even if NODE_DATA(nid)==NULL
Then, what's we need is making policy->mems_allowed be aware of N_HIGH_MEMORY.
This patch does that. But to do so, extra nodemask will be on statck.
Because I know cpumask has a new interface of CPUMASK_ALLOC(), I added it to node.
This patch stands on old behavior. But I feel this fix itself is just a Band-Aid.
But to do fundametal fix, we have to take care of memory hotplug and it takes time.
(task->mems_allowd should be N_HIGH_MEMORY, I think.)
> > Maybe this is bigger patch than expected, but NODEMASK_ALLOC() will be a way
> > to go, anyway. (even if CPUMASK_ALLOC is not used anyware yet..)
> > Kosaki tested this on ia64 NUMA. thanks.
> >
> > I'll wonder more fundamental fix to tsk->mems_allowed but this patch
> > is enough as a fix for now, I think.
> >
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >
> > mpol_set_nodemask() should be aware of N_HIGH_MEMORY and policy's nodemask
> > should be includes only online nodes.
> > In old behavior, this is guaranteed by frequent reference to cpuset's code.
> > Now, most of them are removed and mempolicy has to check it by itself.
> >
> > To do check, a few nodemask_t will be used for calculating nodemask. But,
> > size of nodemask_t can be big and it's not good to allocate them on stack.
> >
> > Now, cpumask_t has CPUMASK_ALLOC/FREE an easy code for get scratch area.
> > NODEMASK_ALLOC/FREE shoudl be there.
> >
> > Tested-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> > include/linux/nodemask.h | 31 +++++++++++++++++
> > mm/mempolicy.c | 82 ++++++++++++++++++++++++++++++++---------------
> > 2 files changed, 87 insertions(+), 26 deletions(-)
> >
> > Index: task-mems-allowed-fix/include/linux/nodemask.h
> > ===================================================================
> > --- task-mems-allowed-fix.orig/include/linux/nodemask.h
> > +++ task-mems-allowed-fix/include/linux/nodemask.h
> > @@ -82,6 +82,13 @@
> > * to generate slightly worse code. So use a simple one-line #define
> > * for node_isset(), instead of wrapping an inline inside a macro, the
> > * way we do the other calls.
> > + *
> > + * NODEMASK_SCRATCH
> > + * For doing above logical AND, OR, XOR, Remap, etc...the caller tend to be
> > + * necessary to use temporal nodemask_t on stack. But if NODES_SHIFT is large,
> > + * size of nodemask_t can be very big and not suitable for allocating in stack.
> > + * NODEMASK_SCRATCH is a helper for such situaions. See below and CPUMASK_ALLOC
> > + * also.
> > */
> >
> > #include <linux/kernel.h>
> > @@ -473,4 +480,28 @@ static inline int num_node_state(enum no
> > #define for_each_node(node) for_each_node_state(node, N_POSSIBLE)
> > #define for_each_online_node(node) for_each_node_state(node, N_ONLINE)
> >
> > +/*
> > + * For nodemask scrach area.(See CPUMASK_ALLOC() in cpumask.h)
> > + */
> > +
> > +#if NODES_SHIFT > 8 /* nodemask_t > 64 bytes */
> > +#define NODEMASK_ALLOC(x, m) struct x *m = kmalloc(sizeof(*m), GFP_KERNEL)
> > +#define NODEMASK_FREE(m) kfree(m)
> > +#else
> > +#define NODEMASK_ALLOC(x, m) struct x _m, *m = &_m
> > +#define NODEMASK_FREE(m)
> > +#endif
> > +
> > +#define NODEMASK_POINTER(v, m) nodemask_t *v = &(m->v)
> > +
> > +/* A example struture for using NODEMASK_ALLOC, used in mempolicy. */
> > +struct nodemask_scratch {
> > + nodemask_t mask1;
> > + nodemask_t mask2;
> > +};
> > +
> > +#define NODEMASK_SCRATCH(x) NODEMASK_ALLOC(nodemask_scratch, x)
> > +#define NODEMASK_SCRATCH_FREE(x) NODEMASK_FREE(x)
>
> Ick. Ho hum. OK. Such is life.
>
> NODEMASK_POINTER() has no callers and is undocumented and unobvious.
> Can I delete it?
>
Yes. I added it just because CPUMASK_ALLOC() provides that.
(And I don't think it's necessary, either ;)
> > void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol)
> > {
> > int ret;
> > + NODEMASK_SCRATCH(scratch);
> >
> > sp->root = RB_ROOT; /* empty tree == default mempolicy */
> > spin_lock_init(&sp->lock);
> > @@ -1902,19 +1923,22 @@ void mpol_shared_policy_init(struct shar
> > if (mpol) {
> > struct vm_area_struct pvma;
> > struct mempolicy *new;
> > -
> > + if (!scratch)
> > + return;
> > /* contextualize the tmpfs mount point mempolicy */
> > new = mpol_new(mpol->mode, mpol->flags, &mpol->w.user_nodemask);
> > if (IS_ERR(new)) {
> > mpol_put(mpol); /* drop our ref on sb mpol */
> > + NODEMASK_SCRATCH_FREE(scratch);
> > return; /* no valid nodemask intersection */
> > }
> >
> > task_lock(current);
> > - ret = mpol_set_nodemask(new, &mpol->w.user_nodemask);
> > + ret = mpol_set_nodemask(new, &mpol->w.user_nodemask, scratch);
> > task_unlock(current);
> > mpol_put(mpol); /* drop our ref on sb mpol */
> > if (ret) {
> > + NODEMASK_SCRATCH_FREE(scratch);
> > mpol_put(new);
> > return;
> > }
> > @@ -1925,6 +1949,7 @@ void mpol_shared_policy_init(struct shar
> > mpol_set_shared_policy(sp, &pvma, new); /* adds ref */
> > mpol_put(new); /* drop initial ref */
> > }
> > + NODEMASK_SCRATCH_FREE(scratch);
> > }
>
> This function does an unneeded kmalloc/kfree if mpol==NULL.
>
Ah yes, the range is not good.
>
> How's this look?
>
> diff -puN include/linux/nodemask.h~mm-make-set_mempolicympol_interleav-n_high_memory-aware-fix include/linux/nodemask.h
> --- a/include/linux/nodemask.h~mm-make-set_mempolicympol_interleav-n_high_memory-aware-fix
> +++ a/include/linux/nodemask.h
> @@ -84,11 +84,10 @@
> * way we do the other calls.
> *
> * NODEMASK_SCRATCH
> - * For doing above logical AND, OR, XOR, Remap, etc...the caller tend to be
> - * necessary to use temporal nodemask_t on stack. But if NODES_SHIFT is large,
> - * size of nodemask_t can be very big and not suitable for allocating in stack.
> - * NODEMASK_SCRATCH is a helper for such situaions. See below and CPUMASK_ALLOC
> - * also.
> + * When doing above logical AND, OR, XOR, Remap operations the callers tend to
> + * need temporary nodemask_t's on the stack. But if NODES_SHIFT is large,
> + * nodemask_t's consume too much stack space. NODEMASK_SCRATCH is a helper
> + * for such situations. See below and CPUMASK_ALLOC also.
> */
>
> #include <linux/kernel.h>
> @@ -492,8 +491,6 @@ static inline int num_node_state(enum no
> #define NODEMASK_FREE(m)
> #endif
>
> -#define NODEMASK_POINTER(v, m) nodemask_t *v = &(m->v)
> -
> /* A example struture for using NODEMASK_ALLOC, used in mempolicy. */
> struct nodemask_scratch {
> nodemask_t mask1;
> diff -puN mm/mempolicy.c~mm-make-set_mempolicympol_interleav-n_high_memory-aware-fix mm/mempolicy.c
> --- a/mm/mempolicy.c~mm-make-set_mempolicympol_interleav-n_high_memory-aware-fix
> +++ a/mm/mempolicy.c
> @@ -1915,7 +1915,6 @@ restart:
> void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol)
> {
> int ret;
> - NODEMASK_SCRATCH(scratch);
>
> sp->root = RB_ROOT; /* empty tree == default mempolicy */
> spin_lock_init(&sp->lock);
> @@ -1923,6 +1922,8 @@ void mpol_shared_policy_init(struct shar
> if (mpol) {
> struct vm_area_struct pvma;
> struct mempolicy *new;
> + NODEMASK_SCRATCH(scratch);
> +
> if (!scratch)
> return;
> /* contextualize the tmpfs mount point mempolicy */
> @@ -1948,8 +1949,8 @@ void mpol_shared_policy_init(struct shar
> pvma.vm_end = TASK_SIZE; /* policy covers entire file */
> mpol_set_shared_policy(sp, &pvma, new); /* adds ref */
> mpol_put(new); /* drop initial ref */
> + NODEMASK_SCRATCH_FREE(scratch);
> }
> - NODEMASK_SCRATCH_FREE(scratch);
> }
>
> int mpol_set_shared_policy(struct shared_policy *info,
> _
>
Seems nice
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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