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Date: Tue, 20 Apr 2021 18:58:23 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: glittao@...il.com, cl@...ux.com, penberg@...nel.org,
rientjes@...gle.com, iamjoonsoo.kim@....com,
akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/slub: use stackdepot to save stack trace in objects
On 4/14/21 6:34 PM, glittao@...il.com wrote:
> From: Oliver Glitta <glittao@...il.com>
>
> Many stack traces are similar so there are many similar arrays.
> Stackdepot saves each unique stack only once.
>
> Replace field addrs in struct track with depot_stack_handle_t handle.
> Use stackdepot to save stack trace.
>
> The benefits are smaller memory overhead and possibility to aggregate
> per-cache statistics in the future using the stackdepot handle
> instead of matching stacks manually.
>
> Signed-off-by: Oliver Glitta <glittao@...il.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
(again with a disclaimer that I'm the advisor of Oliver's student project)
> ---
> init/Kconfig | 1 +
> mm/slub.c | 79 ++++++++++++++++++++++++++++++++--------------------
> 2 files changed, 50 insertions(+), 30 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 37a17853433a..a4ed2daa6c41 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1891,6 +1891,7 @@ config SLUB_DEBUG
> default y
> bool "Enable SLUB debugging support" if EXPERT
> depends on SLUB && SYSFS
> + select STACKDEPOT if STACKTRACE_SUPPORT
> help
> SLUB has extensive debug support features. Disabling these can
> result in significant savings in code size. This also disables
> diff --git a/mm/slub.c b/mm/slub.c
> index 9c0e26ddf300..4b18499726eb 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -35,6 +35,7 @@
> #include <linux/prefetch.h>
> #include <linux/memcontrol.h>
> #include <linux/random.h>
> +#include <linux/stackdepot.h>
>
> #include <trace/events/kmem.h>
>
> @@ -203,8 +204,8 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
> #define TRACK_ADDRS_COUNT 16
> struct track {
> unsigned long addr; /* Called from address */
> -#ifdef CONFIG_STACKTRACE
> - unsigned long addrs[TRACK_ADDRS_COUNT]; /* Called from address */
> +#ifdef CONFIG_STACKDEPOT
> + depot_stack_handle_t handle;
> #endif
> int cpu; /* Was running on cpu */
> int pid; /* Pid context */
> @@ -581,22 +582,27 @@ static struct track *get_track(struct kmem_cache *s, void *object,
> return kasan_reset_tag(p + alloc);
> }
>
> +#ifdef CONFIG_STACKDEPOT
> +static depot_stack_handle_t save_stack_trace(gfp_t flags)
> +{
> + unsigned long entries[TRACK_ADDRS_COUNT];
> + depot_stack_handle_t handle;
> + unsigned int nr_entries;
> +
> + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 4);
> + handle = stack_depot_save(entries, nr_entries, flags);
> + return handle;
> +}
> +#endif
> +
> static void set_track(struct kmem_cache *s, void *object,
> enum track_item alloc, unsigned long addr)
> {
> struct track *p = get_track(s, object, alloc);
>
> if (addr) {
> -#ifdef CONFIG_STACKTRACE
> - unsigned int nr_entries;
> -
> - metadata_access_enable();
> - nr_entries = stack_trace_save(kasan_reset_tag(p->addrs),
> - TRACK_ADDRS_COUNT, 3);
> - metadata_access_disable();
> -
> - if (nr_entries < TRACK_ADDRS_COUNT)
> - p->addrs[nr_entries] = 0;
> +#ifdef CONFIG_STACKDEPOT
> + p->handle = save_stack_trace(GFP_KERNEL);
> #endif
> p->addr = addr;
> p->cpu = smp_processor_id();
> @@ -623,14 +629,19 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time)
>
> pr_err("%s in %pS age=%lu cpu=%u pid=%d\n",
> s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);
> -#ifdef CONFIG_STACKTRACE
> +#ifdef CONFIG_STACKDEPOT
> {
> - int i;
> - for (i = 0; i < TRACK_ADDRS_COUNT; i++)
> - if (t->addrs[i])
> - pr_err("\t%pS\n", (void *)t->addrs[i]);
> - else
> - break;
> + depot_stack_handle_t handle;
> + unsigned long *entries;
> + unsigned int nr_entries;
> +
> + handle = READ_ONCE(t->handle);
> + if (!handle) {
> + pr_err("object allocation/free stack trace missing\n");
> + } else {
> + nr_entries = stack_depot_fetch(handle, &entries);
> + stack_trace_print(entries, nr_entries, 0);
> + }
> }
> #endif
> }
> @@ -4017,18 +4028,26 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
> objp = fixup_red_left(s, objp);
> trackp = get_track(s, objp, TRACK_ALLOC);
> kpp->kp_ret = (void *)trackp->addr;
> -#ifdef CONFIG_STACKTRACE
> - for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
> - kpp->kp_stack[i] = (void *)trackp->addrs[i];
> - if (!kpp->kp_stack[i])
> - break;
> - }
> +#ifdef CONFIG_STACKDEPOT
> + {
> + depot_stack_handle_t handle;
> + unsigned long *entries;
> + unsigned int nr_entries;
>
> - trackp = get_track(s, objp, TRACK_FREE);
> - for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
> - kpp->kp_free_stack[i] = (void *)trackp->addrs[i];
> - if (!kpp->kp_free_stack[i])
> - break;
> + handle = READ_ONCE(trackp->handle);
> + if (handle) {
> + nr_entries = stack_depot_fetch(handle, &entries);
> + for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
> + kpp->kp_stack[i] = (void *)entries[i];
> + }
> +
> + trackp = get_track(s, objp, TRACK_FREE);
> + handle = READ_ONCE(trackp->handle);
> + if (handle) {
> + nr_entries = stack_depot_fetch(handle, &entries);
> + for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
> + kpp->kp_free_stack[i] = (void *)entries[i];
> + }
> }
> #endif
> #endif
>
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