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Date: Thu, 26 Jan 2017 04:42:51 +0100
From: Mike Galbraith <efault@....de>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
linux-rt-users <linux-rt-users@...r.kernel.org>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [rfc patch-rt] radix-tree: Partially disable memcg accounting
in radix_tree_node_alloc()
On Wed, 2017-01-25 at 16:06 +0100, Sebastian Andrzej Siewior wrote:
> According to the to description of radix_tree_preload() the return code
> of 0 means that the following addition of a single element does not
> fail. But in RT's case this requirement is not fulfilled. There is more
> than just one user of that function. So instead adding an exception here
> and maybe later one someplace else, what about the following patch?
> That testcase you mentioned passes now:
Modulo missing EXPORT_SYMBOL(), yup, works fine.
> > testcases/kernel/syscalls/madvise/madvise06
> > tst_test.c:760: INFO: Timeout per run is 0h 05m 00s
> > madvise06.c:65: INFO: dropping caches
> > madvise06.c:139: INFO: SwapCached (before madvise): 304
> > madvise06.c:153: INFO: SwapCached (after madvise): 309988
> > madvise06.c:155: PASS: Regression test pass
> >
> > Summary:
> > passed 1
> > failed 0
> > skipped 0
> > warnings 0
>
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index f87f87dec84c..277295039c8f 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -289,19 +289,11 @@ unsigned int radix_tree_gang_lookup(struct radix_tree_root *root,
> unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
> > > > > void ***results, unsigned long *indices,
> > > > > unsigned long first_index, unsigned int max_items);
> -#ifdef CONFIG_PREEMPT_RT_FULL
> -static inline int radix_tree_preload(gfp_t gm) { return 0; }
> -static inline int radix_tree_maybe_preload(gfp_t gfp_mask) { return 0; }
> -static inline int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order)
> -{
> -> > return 0;
> -};
> -
> -#else
> int radix_tree_preload(gfp_t gfp_mask);
> int radix_tree_maybe_preload(gfp_t gfp_mask);
> int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order);
> -#endif
> +void radix_tree_preload_end(void);
> +
> void radix_tree_init(void);
> void *radix_tree_tag_set(struct radix_tree_root *root,
> > > > > unsigned long index, unsigned int tag);
> @@ -324,11 +316,6 @@ unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
> int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
> unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item);
>
> -static inline void radix_tree_preload_end(void)
> -{
> -> > preempt_enable_nort();
> -}
> -
> /**
> * struct radix_tree_iter - radix tree iterator state
> *
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 881cc195d85f..e96c6a99f25c 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -36,7 +36,7 @@
> #include
> #include
> #include > > > /* in_interrupt() */
> -
> +#include
>
> /* Number of nodes in fully populated tree of given height */
> static unsigned long height_to_maxnodes[RADIX_TREE_MAX_PATH + 1] __read_mostly;
> @@ -68,6 +68,7 @@ struct radix_tree_preload {
> > > struct radix_tree_node *nodes;
> };
> static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
> +static DEFINE_LOCAL_IRQ_LOCK(radix_tree_preloads_lock);
>
> static inline void *node_to_entry(void *ptr)
> {
> @@ -290,14 +291,14 @@ radix_tree_node_alloc(struct radix_tree_root *root)
> > > > * succeed in getting a node here (and never reach
> > > > * kmem_cache_alloc)
> > > > */
> -> > > rtp = &get_cpu_var(radix_tree_preloads);
> +> > > rtp = &get_locked_var(radix_tree_preloads_lock, radix_tree_preloads);
> > > > if (rtp->nr) {
> > > > > ret = rtp->nodes;
> > > > > rtp->nodes = ret->private_data;
> > > > > ret->private_data = NULL;
> > > > > rtp->nr--;
> > > > }
> -> > > put_cpu_var(radix_tree_preloads);
> +> > > put_locked_var(radix_tree_preloads_lock, radix_tree_preloads);
> > > > /*
> > > > * Update the allocation stack trace as this is more useful
> > > > * for debugging.
> @@ -337,7 +338,6 @@ radix_tree_node_free(struct radix_tree_node *node)
> > > call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
> }
>
> -#ifndef CONFIG_PREEMPT_RT_FULL
> /*
> * Load up this CPU's radix_tree_node buffer with sufficient objects to
> * ensure that the addition of a single element in the tree cannot fail. On
> @@ -359,14 +359,14 @@ static int __radix_tree_preload(gfp_t gfp_mask, int nr)
> > > */
> > > gfp_mask &= ~__GFP_ACCOUNT;
>
> -> > preempt_disable();
> +> > local_lock(radix_tree_preloads_lock);
> > > rtp = this_cpu_ptr(&radix_tree_preloads);
> > > while (rtp->nr < nr) {
> -> > > preempt_enable();
> +> > > local_unlock(radix_tree_preloads_lock);
> > > > node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
> > > > if (node == NULL)
> > > > > goto out;
> -> > > preempt_disable();
> +> > > local_lock(radix_tree_preloads_lock);
> > > > rtp = this_cpu_ptr(&radix_tree_preloads);
> > > > if (rtp->nr < nr) {
> > > > > node->private_data = rtp->nodes;
> @@ -408,7 +408,7 @@ int radix_tree_maybe_preload(gfp_t gfp_mask)
> > > if (gfpflags_allow_blocking(gfp_mask))
> > > > return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
> > > /* Preloading doesn't help anything with this gfp mask, skip it */
> -> > preempt_disable();
> +> > local_lock(radix_tree_preloads_lock);
> > > return 0;
> }
> EXPORT_SYMBOL(radix_tree_maybe_preload);
> @@ -424,7 +424,7 @@ int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order)
>
> > > /* Preloading doesn't help anything with this gfp mask, skip it */
> > > if (!gfpflags_allow_blocking(gfp_mask)) {
> -> > > preempt_disable();
> +> > > local_lock(radix_tree_preloads_lock);
> > > > return 0;
> > > }
>
> @@ -457,7 +457,11 @@ int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order)
>
> > > return __radix_tree_preload(gfp_mask, nr_nodes);
> }
> -#endif
> +
> +void radix_tree_preload_end(void)
> +{
> +> > local_unlock(radix_tree_preloads_lock);
> +}
>
> /*
> * The maximum index which can be stored in a radix tree
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