On Fri 09-08-13 14:13:51, Kirill A. Shutemov wrote:
> Jan Kara wrote:
> > On Thu 08-08-13 11:45:05, Kirill A. Shutemov wrote:
> > > From 35ba5687ea7aea98645da34ddd0be01a9de8b32d Mon Sep 17 00:00:00 2001
> > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > Date: Wed, 9 Jan 2013 13:25:47 +0200
> > > Subject: [PATCH] radix-tree: implement preload for multiple contiguous
> > > elements
> > >
> > > The radix tree is variable-height, so an insert operation not only has
> > > to build the branch to its corresponding item, it also has to build the
> > > branch to existing items if the size has to be increased (by
> > > radix_tree_extend).
> > >
> > > The worst case is a zero height tree with just a single item at index 0,
> > > and then inserting an item at index ULONG_MAX. This requires 2 new branches
> > > of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
> > >
> > > Radix tree is usually protected by spin lock. It means we want to
> > > pre-allocate required memory before taking the lock.
> > >
> > > Currently radix_tree_preload() only guarantees enough nodes to insert
> > > one element. It's a hard limit. For transparent huge page cache we want
> > > to insert HPAGE_PMD_NR (512 on x86-64) entries to address_space at once.
> > >
> > > This patch introduces radix_tree_preload_count(). It allows to
> > > preallocate nodes enough to insert a number of *contiguous* elements.
> > > The feature costs about 9KiB per-CPU on x86_64, details below.
> > >
> > > Preload uses per-CPU array to store nodes. The total cost of preload is
> > > "array size" * sizeof(void*) * NR_CPUS. We want to increase array size
> > > to be able to handle 512 entries at once.
> > >
> > > Size of array depends on system bitness and on RADIX_TREE_MAP_SHIFT.
> > >
> > > We have three possible RADIX_TREE_MAP_SHIFT:
> > >
> > > #ifdef __KERNEL__
> > > #define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6)
> > > #else
> > > #define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
> > > #endif
> > >
> > > We are not going to use transparent huge page cache on small machines or
> > > in userspace, so we are interested in RADIX_TREE_MAP_SHIFT=6.
> > >
> > > On 64-bit system old array size is 21, new is 37. Per-CPU feature
> > > overhead is
> > > for preload array:
> > > (37 - 21) * sizeof(void*) = 128 bytes
> > > plus, if the preload array is full
> > > (37 - 21) * sizeof(struct radix_tree_node) = 16 * 560 = 8960 bytes
> > > total: 9088 bytes
> > >
> > > On 32-bit system old array size is 11, new is 22. Per-CPU feature
> > > overhead is
> > > for preload array:
> > > (22 - 11) * sizeof(void*) = 44 bytes
> > > plus, if the preload array is full
> > > (22 - 11) * sizeof(struct radix_tree_node) = 11 * 296 = 3256 bytes
> > > total: 3300 bytes
> > >
> > > Since only THP uses batched preload at the moment, we disable (set max
> > > preload to 1) it if !CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE. This can be
> > > changed in the future.
> > >
> > > Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > > ---
> > > include/linux/radix-tree.h | 11 ++++++
> > > lib/radix-tree.c | 89 +++++++++++++++++++++++++++++++++++++++++-----
> > > 2 files changed, 91 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> > > index 4039407..3bf0b3e 100644
> > > --- a/include/linux/radix-tree.h
> > > +++ b/include/linux/radix-tree.h
> > > @@ -83,6 +83,16 @@ do { \
> > > (root)->rnode = NULL; \
> > > } while (0)
> > >
> > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
> > > +/*
> > > + * At the moment only THP uses preload for more then on item for batched
> > > + * pagecache manipulations.
> > > + */
> > > +#define RADIX_TREE_PRELOAD_NR 512
> > > +#else
> > > +#define RADIX_TREE_PRELOAD_NR 1
> > > +#endif
> > > +
> > > /**
> > > * Radix-tree synchronization
> > > *
> > > @@ -232,6 +242,7 @@ unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
> > > unsigned long index, unsigned long max_scan);
> > > int radix_tree_preload(gfp_t gfp_mask);
> > > int radix_tree_maybe_preload(gfp_t gfp_mask);
> > > +int radix_tree_maybe_preload_contig(unsigned size, gfp_t gfp_mask);
> > > void radix_tree_init(void);
> > > void *radix_tree_tag_set(struct radix_tree_root *root,
> > > unsigned long index, unsigned int tag);
> > > diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> > > index 7811ed3..980e4c4 100644
> > > --- a/lib/radix-tree.c
> > > +++ b/lib/radix-tree.c
> > > @@ -84,14 +84,54 @@ static struct kmem_cache *radix_tree_node_cachep;
> > > * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
> > > * Hence:
> > > */
> > > -#define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
> > > +#define RADIX_TREE_PRELOAD_MIN (RADIX_TREE_MAX_PATH * 2 - 1)
> > > +
> > > +/*
> > > + * Inserting N contiguous items is more complex. To simplify calculation, let's
> > > + * limit N (validated in radix_tree_init()):
> > > + * - N is multiplier of RADIX_TREE_MAP_SIZE (or 1);
> > Is this limitation really worth the one reserved item you save?
>
> It's not really limitation, It just doesn't make any sense to lower
> RADIX_TREE_PRELOAD_NR not to RADIX_TREE_MAP_SIZE boundary, since we will
> have to round it up anyway.
>
> I made one more mistake: I've modeled not the situation I've describe, so
> last -1 is wrong. Fixed in patch below.
>
> > > -static int __radix_tree_preload(gfp_t gfp_mask)
> > > +static int __radix_tree_preload_contig(unsigned size, gfp_t gfp_mask)
> > > {
> > > struct radix_tree_preload *rtp;
> > > struct radix_tree_node *node;
> > > int ret = -ENOMEM;
> > > + int preload_target = RADIX_TREE_PRELOAD_MIN +
> > > + DIV_ROUND_UP(size - 1, RADIX_TREE_MAP_SIZE);
> > So you should also warn if size % RADIX_TREE_MAP_SIZE != 0, right?
>
> I've reworked logic here to match RADIX_TREE_PRELOAD_MAX calculation math.
>
> > Otherwise the patch looks fine.
>
> Ack?
Yes. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> From 0e7d481093a4ded0dfb58e87d4edda003f3b2fd6 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Wed, 9 Jan 2013 13:25:47 +0200
> Subject: [PATCH] radix-tree: implement preload for multiple contiguous
> elements
>
> The radix tree is variable-height, so an insert operation not only has
> to build the branch to its corresponding item, it also has to build the
> branch to existing items if the size has to be increased (by
> radix_tree_extend).
>
> The worst case is a zero height tree with just a single item at index 0,
> and then inserting an item at index ULONG_MAX. This requires 2 new branches
> of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
>
> Radix tree is usually protected by spin lock. It means we want to
> pre-allocate required memory before taking the lock.
>
> Currently radix_tree_preload() only guarantees enough nodes to insert
> one element. It's a hard limit. For transparent huge page cache we want
> to insert HPAGE_PMD_NR (512 on x86-64) entries to address_space at once.
>
> This patch introduces radix_tree_preload_count(). It allows to
> preallocate nodes enough to insert a number of *contiguous* elements.
> The feature costs about 9.5KiB per-CPU on x86_64, details below.
>
> Preload uses per-CPU array to store nodes. The total cost of preload is
> "array size" * sizeof(void*) * NR_CPUS. We want to increase array size
> to be able to handle 512 entries at once.
>
> Size of array depends on system bitness and on RADIX_TREE_MAP_SHIFT.
>
> We have three possible RADIX_TREE_MAP_SHIFT:
>
> #ifdef __KERNEL__
> #define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6)
> #else
> #define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
> #endif
>
> We are not going to use transparent huge page cache on small machines or
> in userspace, so we are interested in RADIX_TREE_MAP_SHIFT=6.
>
> On 64-bit system old array size is 21, new is 37. Per-CPU feature
> overhead is
> for preload array:
> (38 - 21) * sizeof(void*) = 136 bytes
> plus, if the preload array is full
> (38 - 21) * sizeof(struct radix_tree_node) = 17 * 560 = 9520 bytes
> total: 9656 bytes
>
> On 32-bit system old array size is 11, new is 22. Per-CPU feature
> overhead is
> for preload array:
> (23 - 11) * sizeof(void*) = 48 bytes
> plus, if the preload array is full
> (23 - 11) * sizeof(struct radix_tree_node) = 12 * 296 = 3552 bytes
> total: 3600 bytes
>
> Since only THP uses batched preload at the moment, we disable (set max
> preload to 1) it if !CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE. This can be
> changed in the future.
>
> Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> ---
> include/linux/radix-tree.h | 11 ++++++
> lib/radix-tree.c | 95 +++++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 97 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 4039407..3bf0b3e 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -83,6 +83,16 @@ do { \
> (root)->rnode = NULL; \
> } while (0)
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
> +/*
> + * At the moment only THP uses preload for more then on item for batched
> + * pagecache manipulations.
> + */
> +#define RADIX_TREE_PRELOAD_NR 512
> +#else
> +#define RADIX_TREE_PRELOAD_NR 1
> +#endif
> +
> /**
> * Radix-tree synchronization
> *
> @@ -232,6 +242,7 @@ unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
> unsigned long index, unsigned long max_scan);
> int radix_tree_preload(gfp_t gfp_mask);
> int radix_tree_maybe_preload(gfp_t gfp_mask);
> +int radix_tree_maybe_preload_contig(unsigned size, gfp_t gfp_mask);
> void radix_tree_init(void);
> void *radix_tree_tag_set(struct radix_tree_root *root,
> unsigned long index, unsigned int tag);
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 7811ed3..1c19595 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -84,14 +84,52 @@ static struct kmem_cache *radix_tree_node_cachep;
> * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
> * Hence:
> */
> -#define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
> +#define RADIX_TREE_PRELOAD_MIN (RADIX_TREE_MAX_PATH * 2 - 1)
> +
> +/*
> + * Inserting N contiguous items is more complex. To simplify calculation, let's
> + * limit N (validated in radix_tree_init()):
> + * - N is multiplier of RADIX_TREE_MAP_SIZE (or 1);
> + * - N <= number of items 2-level tree can contain:
> + * 1UL << (2 * RADIX_TREE_MAP_SHIFT).
> + *
> + * No limitation on insert index alignment.
> + *
> + * Then the worst case is tree with only one element at index 0 and we add N
> + * items where at least one index requires max tree high and we cross boundary
> + * between items in root node.
> + *
> + * Basically, at least one index is less then
> + *
> + * 1UL << ((RADIX_TREE_MAX_PATH - 1) * RADIX_TREE_MAP_SHIFT)
> + *
> + * and one is equal to.
> + *
> + * In this case we need:
> + *
> + * - RADIX_TREE_MAX_PATH nodes to build new path to item with index 0;
> + * - N / RADIX_TREE_MAP_SIZE + 1 nodes for last level nodes for new items:
> + * - +1 is for misalinged case;
> + * - 2 * (RADIX_TREE_MAX_PATH - 2) - 1 nodes to build path to last level nodes:
> + * - -2, because root node and last level nodes are already accounted).
> + *
> + * Hence:
> + */
> +#if RADIX_TREE_PRELOAD_NR > 1
> +#define RADIX_TREE_PRELOAD_MAX \
> + ( RADIX_TREE_MAX_PATH + \
> + RADIX_TREE_PRELOAD_NR / RADIX_TREE_MAP_SIZE + 1 + \
> + 2 * (RADIX_TREE_MAX_PATH - 2))
> +#else
> +#define RADIX_TREE_PRELOAD_MAX RADIX_TREE_PRELOAD_MIN
> +#endif
>
> /*
> * Per-cpu pool of preloaded nodes
> */
> struct radix_tree_preload {
> int nr;
> - struct radix_tree_node *nodes[RADIX_TREE_PRELOAD_SIZE];
> + struct radix_tree_node *nodes[RADIX_TREE_PRELOAD_MAX];
> };
> static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
>
> @@ -263,29 +301,43 @@ radix_tree_node_free(struct radix_tree_node *node)
>
> /*
> * 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
> - * success, return zero, with preemption disabled. On error, return -ENOMEM
> + * ensure that the addition of *contiguous* items in the tree cannot fail.
> + * On success, return zero, with preemption disabled. On error, return -ENOMEM
> * with preemption not disabled.
> *
> * To make use of this facility, the radix tree must be initialised without
> * __GFP_WAIT being passed to INIT_RADIX_TREE().
> */
> -static int __radix_tree_preload(gfp_t gfp_mask)
> +static int __radix_tree_preload_contig(unsigned size, gfp_t gfp_mask)
> {
> struct radix_tree_preload *rtp;
> struct radix_tree_node *node;
> int ret = -ENOMEM;
> + int preload_target = RADIX_TREE_PRELOAD_MIN;
>
> + if (size > 1) {
> + size = round_up(size, RADIX_TREE_MAP_SIZE);
> + if (WARN_ONCE(size > RADIX_TREE_PRELOAD_NR,
> + "too large preload requested"))
> + return -ENOMEM;
> +
> + /* The same math as with RADIX_TREE_PRELOAD_MAX */
> + preload_target = RADIX_TREE_MAX_PATH +
> + size / RADIX_TREE_MAP_SIZE + 1 +
> + 2 * (RADIX_TREE_MAX_PATH - 2);
> + }
> +
> + BUG_ON(preload_target > RADIX_TREE_PRELOAD_MAX);
> preempt_disable();
> rtp = &__get_cpu_var(radix_tree_preloads);
> - while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
> + while (rtp->nr < preload_target) {
> preempt_enable();
> node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
> if (node == NULL)
> goto out;
> preempt_disable();
> rtp = &__get_cpu_var(radix_tree_preloads);
> - if (rtp->nr < ARRAY_SIZE(rtp->nodes))
> + if (rtp->nr < preload_target)
> rtp->nodes[rtp->nr++] = node;
> else
> kmem_cache_free(radix_tree_node_cachep, node);
> @@ -308,7 +360,7 @@ int radix_tree_preload(gfp_t gfp_mask)
> {
> /* Warn on non-sensical use... */
> WARN_ON_ONCE(!(gfp_mask & __GFP_WAIT));
> - return __radix_tree_preload(gfp_mask);
> + return __radix_tree_preload_contig(1, gfp_mask);
> }
> EXPORT_SYMBOL(radix_tree_preload);
>
> @@ -320,13 +372,22 @@ EXPORT_SYMBOL(radix_tree_preload);
> int radix_tree_maybe_preload(gfp_t gfp_mask)
> {
> if (gfp_mask & __GFP_WAIT)
> - return __radix_tree_preload(gfp_mask);
> + return __radix_tree_preload_contig(1, gfp_mask);
> /* Preloading doesn't help anything with this gfp mask, skip it */
> preempt_disable();
> return 0;
> }
> EXPORT_SYMBOL(radix_tree_maybe_preload);
>
> +int radix_tree_maybe_preload_contig(unsigned size, gfp_t gfp_mask)
> +{
> + if (gfp_mask & __GFP_WAIT)
> + return __radix_tree_preload_contig(size, gfp_mask);
> + /* Preloading doesn't help anything with this gfp mask, skip it */
> + preempt_disable();
> + return 0;
> +}
> +
> /*
> * Return the maximum key which can be store into a
> * radix tree with height HEIGHT.
> @@ -1483,6 +1544,22 @@ static int radix_tree_callback(struct notifier_block *nfb,
>
> void __init radix_tree_init(void)
> {
> + /*
> + * Restrictions on RADIX_TREE_PRELOAD_NR simplify RADIX_TREE_PRELOAD_MAX
> + * calculation, it's already complex enough:
> + * - it must be multiplier of RADIX_TREE_MAP_SIZE, otherwise we will
> + * have to round it up to next RADIX_TREE_MAP_SIZE multiplier and we
> + * don't win anything;
> + * - must be less then number of items 2-level tree can contain.
> + * It's easier to calculate number of internal nodes required
> + * this way.
> + */
> + if (RADIX_TREE_PRELOAD_NR != 1) {
> + BUILD_BUG_ON(RADIX_TREE_PRELOAD_NR % RADIX_TREE_MAP_SIZE != 0);
> + BUILD_BUG_ON(RADIX_TREE_PRELOAD_NR >
> + 1UL << (2 * RADIX_TREE_MAP_SHIFT));
> + }
> +
> radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
> sizeof(struct radix_tree_node), 0,
> SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
> --
> Kirill A. Shutemov
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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