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Message-Id: <20221115005633.4bcc987ae18e06d250770dd7@kernel.org>
Date: Tue, 15 Nov 2022 00:56:33 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: wuqiang <wuqiang.matt@...edance.com>
Cc: davem@...emloft.net, anil.s.keshavamurthy@...el.com,
naveen.n.rao@...ux.ibm.com, rostedt@...dmis.org,
peterz@...radead.org, akpm@...ux-foundation.org,
sander@...nheule.net, ebiggers@...gle.com,
dan.j.williams@...el.com, jpoimboe@...nel.org,
linux-kernel@...r.kernel.org, lkp@...el.com, mattwu@....com
Subject: Re: [PATCH v6 3/4] kprobes: kretprobe scalability improvement with
objpool
Hi Wuqiang,
On Tue, 8 Nov 2022 15:14:42 +0800
wuqiang <wuqiang.matt@...edance.com> wrote:
> kretprobe is using freelist to manage return-instances, but freelist,
> as LIFO queue based on singly linked list, scales badly and reduces
> the overall throughput of kretprobed routines, especially for high
> contention scenarios.
>
> Here's a typical throughput test of sys_flock (counts in 10 seconds,
> measured with perf stat -a -I 10000 -e syscalls:sys_enter_flock):
>
> OS: Debian 10 X86_64, Linux 6.1rc2
> HW: XEON 8336C x 2, 64 cores/128 threads, DDR4 3200MT/s
>
> 1X 2X 4X 6X 8X 12X 16X
> 34762430 36546920 17949900 13101899 12569595 12646601 14729195
> 24X 32X 48X 64X 72X 96X 128X
> 19263546 10102064 8985418 11936495 11493980 7127789 9330985
>
> This patch introduces objpool to kretprobe and rethook, with orginal
> freelist replaced and brings near-linear scalability to kretprobed
> routines. Tests of kretprobe throughput show the biggest ratio as
> 333.9x of the original freelist. Here's the comparison:
>
> 1X 2X 4X 8X 16X
> freelist: 34762430 36546920 17949900 12569595 14729195
> objpool: 35627544 72182095 144068494 287564688 576903916
> 32X 48X 64X 96X 128X
> freelist: 10102064 8985418 11936495 7127789 9330985
> objpool: 1158876372 1737828164 2324371724 2380310472 2463182819
>
> Tests on 96-core ARM64 system output similarly, but with the biggest
> ratio up to 642.2x:
>
> OS: Debian 10 AARCH64, Linux 6.1rc2
> HW: Kunpeng-920 96 cores/2 sockets/4 NUMA nodes, DDR4 2933 MT/s
>
> 1X 2X 4X 8X 16X
> freelist: 17498299 10887037 10224710 8499132 6421751
> objpool: 18715726 35549845 71615884 144258971 283707220
> 24X 32X 48X 64X 96X
> freelist: 5339868 4819116 3593919 3121575 2687167
> objpool: 419830913 571609748 877456139 1143316315 1725668029
>
> Signed-off-by: wuqiang <wuqiang.matt@...edance.com>
> ---
> include/linux/kprobes.h | 9 ++--
> include/linux/rethook.h | 15 +++----
> kernel/kprobes.c | 95 +++++++++++++++++++----------------------
> kernel/trace/fprobe.c | 17 ++------
> kernel/trace/rethook.c | 80 +++++++++++++++++-----------------
> 5 files changed, 95 insertions(+), 121 deletions(-)
>
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index a0b92be98984..f13f01e600c2 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -27,7 +27,7 @@
> #include <linux/mutex.h>
> #include <linux/ftrace.h>
> #include <linux/refcount.h>
> -#include <linux/freelist.h>
> +#include <linux/objpool.h>
> #include <linux/rethook.h>
> #include <asm/kprobes.h>
>
> @@ -141,6 +141,7 @@ static inline bool kprobe_ftrace(struct kprobe *p)
> */
> struct kretprobe_holder {
> struct kretprobe *rp;
> + struct objpool_head oh;
Could you rename it to `pool` as rethook does?
> refcount_t ref;
> };
>
> @@ -154,7 +155,6 @@ struct kretprobe {
> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
> struct rethook *rh;
> #else
> - struct freelist_head freelist;
OK, this is natural to move the head to kretprobe_holder, because
objpool must call its fini() function when all objects are freed.
> struct kretprobe_holder *rph;
> #endif
> };
> @@ -165,10 +165,7 @@ struct kretprobe_instance {
> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
> struct rethook_node node;
> #else
> - union {
> - struct freelist_node freelist;
> - struct rcu_head rcu;
> - };
> + struct rcu_head rcu;
> struct llist_node llist;
> struct kretprobe_holder *rph;
> kprobe_opcode_t *ret_addr;
> diff --git a/include/linux/rethook.h b/include/linux/rethook.h
> index c8ac1e5afcd1..278ec65e71fe 100644
> --- a/include/linux/rethook.h
> +++ b/include/linux/rethook.h
> @@ -6,7 +6,7 @@
> #define _LINUX_RETHOOK_H
>
> #include <linux/compiler.h>
> -#include <linux/freelist.h>
> +#include <linux/objpool.h>
> #include <linux/kallsyms.h>
> #include <linux/llist.h>
> #include <linux/rcupdate.h>
> @@ -30,14 +30,14 @@ typedef void (*rethook_handler_t) (struct rethook_node *, void *, struct pt_regs
> struct rethook {
> void *data;
> rethook_handler_t handler;
> - struct freelist_head pool;
> + struct objpool_head pool;
On the other hand, the rethook already consolidated that "holder"
feature to itself, so you don't need to move, just replace the
freelist_head with objpool_head. LGTM.
> refcount_t ref;
> struct rcu_head rcu;
> };
>
> /**
> * struct rethook_node - The rethook shadow-stack entry node.
> - * @freelist: The freelist, linked to struct rethook::pool.
> + * @nod: The objpool node, linked to struct rethook::pool.
I don't see @nod in rethook_node. maybe a typo?
> * @rcu: The rcu_head for deferred freeing.
> * @llist: The llist, linked to a struct task_struct::rethooks.
> * @rethook: The pointer to the struct rethook.
> @@ -48,19 +48,15 @@ struct rethook {
> * on each entry of the shadow stack.
> */
> struct rethook_node {
> - union {
> - struct freelist_node freelist;
> - struct rcu_head rcu;
> - };
> + struct rcu_head rcu;
> struct llist_node llist;
> struct rethook *rethook;
> unsigned long ret_addr;
> unsigned long frame;
> };
>
> -struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
> +struct rethook *rethook_alloc(void *data, rethook_handler_t handler, gfp_t gfp, int size, int max);
> void rethook_free(struct rethook *rh);
> -void rethook_add_node(struct rethook *rh, struct rethook_node *node);
> struct rethook_node *rethook_try_get(struct rethook *rh);
> void rethook_recycle(struct rethook_node *node);
> void rethook_hook(struct rethook_node *node, struct pt_regs *regs, bool mcount);
> @@ -97,4 +93,3 @@ void rethook_flush_task(struct task_struct *tk);
> #endif
>
> #endif
> -
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index cd9f5a66a690..a8b202f87e2d 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1865,10 +1865,12 @@ static struct notifier_block kprobe_exceptions_nb = {
> static void free_rp_inst_rcu(struct rcu_head *head)
> {
> struct kretprobe_instance *ri = container_of(head, struct kretprobe_instance, rcu);
> + struct kretprobe_holder *rph = ri->rph;
>
> - if (refcount_dec_and_test(&ri->rph->ref))
> - kfree(ri->rph);
> - kfree(ri);
> + if (refcount_dec_and_test(&rph->ref)) {
> + objpool_fini(&rph->oh);
> + kfree(rph);
> + }
> }
> NOKPROBE_SYMBOL(free_rp_inst_rcu);
>
> @@ -1877,7 +1879,7 @@ static void recycle_rp_inst(struct kretprobe_instance *ri)
> struct kretprobe *rp = get_kretprobe(ri);
>
> if (likely(rp))
> - freelist_add(&ri->freelist, &rp->freelist);
> + objpool_push(ri, &rp->rph->oh);
> else
> call_rcu(&ri->rcu, free_rp_inst_rcu);
> }
> @@ -1914,23 +1916,19 @@ NOKPROBE_SYMBOL(kprobe_flush_task);
>
> static inline void free_rp_inst(struct kretprobe *rp)
> {
> - struct kretprobe_instance *ri;
> - struct freelist_node *node;
> - int count = 0;
> -
> - node = rp->freelist.head;
> - while (node) {
> - ri = container_of(node, struct kretprobe_instance, freelist);
> - node = node->next;
> -
> - kfree(ri);
> - count++;
> - }
> + struct kretprobe_holder *rph = rp->rph;
> + void *nod;
>
> - if (refcount_sub_and_test(count, &rp->rph->ref)) {
> - kfree(rp->rph);
> - rp->rph = NULL;
> - }
> + rp->rph = NULL;
> + do {
> + nod = objpool_pop(&rph->oh);
> + /* deref anyway since we've one extra ref grabbed */
> + if (refcount_dec_and_test(&rph->ref)) {
> + objpool_fini(&rph->oh);
> + kfree(rph);
> + break;
> + }
> + } while (nod);
> }
>
> /* This assumes the 'tsk' is the current task or the is not running. */
> @@ -2072,19 +2070,17 @@ NOKPROBE_SYMBOL(__kretprobe_trampoline_handler)
> static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
> {
> struct kretprobe *rp = container_of(p, struct kretprobe, kp);
> + struct kretprobe_holder *rph = rp->rph;
> struct kretprobe_instance *ri;
> - struct freelist_node *fn;
>
> - fn = freelist_try_get(&rp->freelist);
> - if (!fn) {
> + ri = objpool_pop(&rph->oh);
> + if (!ri) {
> rp->nmissed++;
> return 0;
> }
>
> - ri = container_of(fn, struct kretprobe_instance, freelist);
> -
> if (rp->entry_handler && rp->entry_handler(ri, regs)) {
> - freelist_add(&ri->freelist, &rp->freelist);
> + objpool_push(ri, &rph->oh);
> return 0;
> }
>
> @@ -2174,10 +2170,19 @@ int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long o
> return 0;
> }
>
> +#ifndef CONFIG_KRETPROBE_ON_RETHOOK
> +static int kretprobe_init_inst(void *context, void *nod)
> +{
> + struct kretprobe_instance *ri = nod;
> +
> + ri->rph = context;
> + return 0;
> +}
> +#endif
> +
> int register_kretprobe(struct kretprobe *rp)
> {
> int ret;
> - struct kretprobe_instance *inst;
> int i;
> void *addr;
>
> @@ -2215,20 +2220,12 @@ int register_kretprobe(struct kretprobe *rp)
> #endif
> }
> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
> - rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler);
> + rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler, GFP_KERNEL,
> + sizeof(struct kretprobe_instance) + rp->data_size,
> + rp->maxactive);
> if (!rp->rh)
> return -ENOMEM;
>
> - for (i = 0; i < rp->maxactive; i++) {
> - inst = kzalloc(sizeof(struct kretprobe_instance) +
> - rp->data_size, GFP_KERNEL);
> - if (inst == NULL) {
> - rethook_free(rp->rh);
> - rp->rh = NULL;
> - return -ENOMEM;
> - }
> - rethook_add_node(rp->rh, &inst->node);
> - }
> rp->nmissed = 0;
> /* Establish function entry probe point */
> ret = register_kprobe(&rp->kp);
> @@ -2237,25 +2234,19 @@ int register_kretprobe(struct kretprobe *rp)
> rp->rh = NULL;
> }
> #else /* !CONFIG_KRETPROBE_ON_RETHOOK */
> - rp->freelist.head = NULL;
> rp->rph = kzalloc(sizeof(struct kretprobe_holder), GFP_KERNEL);
> if (!rp->rph)
> return -ENOMEM;
>
> - rp->rph->rp = rp;
> - for (i = 0; i < rp->maxactive; i++) {
> - inst = kzalloc(sizeof(struct kretprobe_instance) +
> - rp->data_size, GFP_KERNEL);
> - if (inst == NULL) {
> - refcount_set(&rp->rph->ref, i);
> - free_rp_inst(rp);
> - return -ENOMEM;
> - }
> - inst->rph = rp->rph;
> - freelist_add(&inst->freelist, &rp->freelist);
> + if (objpool_init(&rp->rph->oh, rp->maxactive, rp->maxactive,
> + rp->data_size + sizeof(struct kretprobe_instance),
> + GFP_KERNEL, rp->rph, kretprobe_init_inst, NULL)) {
> + kfree(rp->rph);
> + rp->rph = NULL;
> + return -ENOMEM;
> }
> - refcount_set(&rp->rph->ref, i);
> -
> + refcount_set(&rp->rph->ref, rp->maxactive + 1);
> + rp->rph->rp = rp;
> rp->nmissed = 0;
> /* Establish function entry probe point */
> ret = register_kprobe(&rp->kp);
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index e8143e368074..9a002bfbd216 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -125,7 +125,7 @@ static void fprobe_init(struct fprobe *fp)
>
> static int fprobe_init_rethook(struct fprobe *fp, int num)
> {
> - int i, size;
> + int size;
>
> if (num < 0)
> return -EINVAL;
> @@ -140,20 +140,11 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
> if (size < 0)
> return -E2BIG;
>
> - fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
> + fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler, GFP_KERNEL,
> + sizeof(struct fprobe_rethook_node), size);
> if (!fp->rethook)
> return -ENOMEM;
> - for (i = 0; i < size; i++) {
> - struct fprobe_rethook_node *node;
> -
> - node = kzalloc(sizeof(*node), GFP_KERNEL);
> - if (!node) {
> - rethook_free(fp->rethook);
> - fp->rethook = NULL;
> - return -ENOMEM;
> - }
> - rethook_add_node(fp->rethook, &node->node);
> - }
> +
> return 0;
> }
>
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index c69d82273ce7..01df98db2fbe 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -36,21 +36,17 @@ void rethook_flush_task(struct task_struct *tk)
> static void rethook_free_rcu(struct rcu_head *head)
> {
> struct rethook *rh = container_of(head, struct rethook, rcu);
> - struct rethook_node *rhn;
> - struct freelist_node *node;
> - int count = 1;
> + struct rethook_node *nod;
>
> - node = rh->pool.head;
> - while (node) {
> - rhn = container_of(node, struct rethook_node, freelist);
> - node = node->next;
> - kfree(rhn);
> - count++;
> - }
> -
> - /* The rh->ref is the number of pooled node + 1 */
> - if (refcount_sub_and_test(count, &rh->ref))
> - kfree(rh);
> + do {
> + nod = objpool_pop(&rh->pool);
> + /* deref anyway since we've one extra ref grabbed */
> + if (refcount_dec_and_test(&rh->ref)) {
> + objpool_fini(&rh->pool);
> + kfree(rh);
> + break;
> + }
> + } while (nod);
> }
>
> /**
> @@ -70,16 +66,28 @@ void rethook_free(struct rethook *rh)
> call_rcu(&rh->rcu, rethook_free_rcu);
> }
>
> +static int rethook_init_node(void *context, void *nod)
> +{
> + struct rethook_node *node = nod;
> +
> + node->rethook = context;
> + return 0;
> +}
> +
> /**
> * rethook_alloc() - Allocate struct rethook.
> * @data: a data to pass the @handler when hooking the return.
> * @handler: the return hook callback function.
> + * @gfp: default gfp for objpool allocation
> + * @size: rethook node size
@size should be @data_size, which is the size of additional data bytes
of rethook_node.
> + * @max: number of rethook nodes to be preallocated
> *
> * Allocate and initialize a new rethook with @data and @handler.
> * Return NULL if memory allocation fails or @handler is NULL.
> * Note that @handler == NULL means this rethook is going to be freed.
> */
> -struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
> +struct rethook *rethook_alloc(void *data, rethook_handler_t handler, gfp_t gfp,
> + int size, int max)
This doesn't need @gfp. Just use GFP_KERNEL from rethook layer.
> {
> struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
And here,
if (data_size < 0 || max < 0)
return -EINVAL;
>
> @@ -88,34 +96,26 @@ struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
>
> rh->data = data;
> rh->handler = handler;
> - rh->pool.head = NULL;
> - refcount_set(&rh->ref, 1);
>
> + /* initialize the objpool for rethook nodes */
> + if (objpool_init(&rh->pool, max, max, size, gfp, rh, rethook_init_node,
> + NULL)) {
> + kfree(rh);
> + return NULL;
> + }
> + refcount_set(&rh->ref, max + 1);
> return rh;
> }
>
> -/**
> - * rethook_add_node() - Add a new node to the rethook.
> - * @rh: the struct rethook.
> - * @node: the struct rethook_node to be added.
> - *
> - * Add @node to @rh. User must allocate @node (as a part of user's
> - * data structure.) The @node fields are initialized in this function.
> - */
> -void rethook_add_node(struct rethook *rh, struct rethook_node *node)
> -{
> - node->rethook = rh;
> - freelist_add(&node->freelist, &rh->pool);
> - refcount_inc(&rh->ref);
> -}
> -
> static void free_rethook_node_rcu(struct rcu_head *head)
> {
> struct rethook_node *node = container_of(head, struct rethook_node, rcu);
> + struct rethook *rh = node->rethook;
>
> - if (refcount_dec_and_test(&node->rethook->ref))
> - kfree(node->rethook);
> - kfree(node);
> + if (refcount_dec_and_test(&rh->ref)) {
> + objpool_fini(&rh->pool);
> + kfree(rh);
> + }
> }
>
> /**
> @@ -130,7 +130,7 @@ void rethook_recycle(struct rethook_node *node)
> lockdep_assert_preemption_disabled();
>
> if (likely(READ_ONCE(node->rethook->handler)))
> - freelist_add(&node->freelist, &node->rethook->pool);
> + objpool_push(node, &node->rethook->pool);
> else
> call_rcu(&node->rcu, free_rethook_node_rcu);
> }
> @@ -146,7 +146,7 @@ NOKPROBE_SYMBOL(rethook_recycle);
> struct rethook_node *rethook_try_get(struct rethook *rh)
> {
> rethook_handler_t handler = READ_ONCE(rh->handler);
> - struct freelist_node *fn;
> + struct rethook_node *nod;
>
> lockdep_assert_preemption_disabled();
>
> @@ -163,11 +163,11 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
> if (unlikely(!rcu_is_watching()))
> return NULL;
>
> - fn = freelist_try_get(&rh->pool);
> - if (!fn)
> + nod = (struct rethook_node *)objpool_pop(&rh->pool);
> + if (!nod)
> return NULL;
>
> - return container_of(fn, struct rethook_node, freelist);
> + return nod;
You can just write this part as
return (struct rethook_node *)objpool_pop(&rh->pool);
Thank you,
> }
> NOKPROBE_SYMBOL(rethook_try_get);
>
> --
> 2.34.1
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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