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SubjectRe: Allocation failure of ring buffer for trace
On Mon, Nov 13, 2017 at 12:48:36PM -0500, YASUAKI ISHIMATSU wrote:
> When using trace_buf_size= boot option, memory allocation of ring buffer
> for trace fails as follows:
>
> [ ] x86: Booting SMP configuration:
> <SNIP>
>
> In my server, there are 384 CPUs, 512 GB memory and 8 nodes. And
> "trace_buf_size=100M" is set.
>
> When using trace_buf_size=100M, kernel allocates 100 MB memory
> per CPU before calling free_are_init_core(). Kernel tries to
> allocates 38.4GB (100 MB * 384 CPU) memory. But available memory
> at this time is about 16GB (2 GB * 8 nodes) due to the following commit:
>
> 3a80a7fa7989 ("mm: meminit: initialise a subset of struct pages
> if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set")
>

1. What is the use case for such a large trace buffer being allocated at
boot time?
2. Is disabling CONFIG_DEFERRED_STRUCT_PAGE_INIT at compile time an
option for you given that it's a custom-built kernel and not a
distribution kernel?

Basically, as the allocation context is within smp_init(), there are no
opportunities to do the deferred meminit early. Furthermore, the partial
initialisation of memory occurs before the size of the trace buffers is
set so there is no opportunity to adjust the amount of memory that is
pre-initialised. We could potentially catch when memory is low during
system boot and adjust the amount that is initialised serially but the
complexity would be high. Given that deferred meminit is basically a minor
optimisation that only affects very large machines and trace_buf_size being
used is somewhat specialised, I think the most straight-forward option is
to go back to serialised meminit if trace_buf_size is specified like this;

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 710143741eb5..6ef0ab13f774 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -558,6 +558,19 @@ void drain_local_pages(struct zone *zone);

void page_alloc_init_late(void);

+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+extern void __init disable_deferred_meminit(void);
+extern void page_alloc_init_late_prepare(void);
+#else
+static inline void disable_deferred_meminit(void)
+{
+}
+
+static inline void page_alloc_init_late_prepare(void)
+{
+}
+#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
+
/*
* gfp_allowed_mask is set to GFP_BOOT_MASK during early boot to restrict what
* GFP flags are used before interrupts are enabled. Once interrupts are
diff --git a/init/main.c b/init/main.c
index 0ee9c6866ada..0248b8b5bc3a 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1058,6 +1058,8 @@ static noinline void __init kernel_init_freeable(void)
do_pre_smp_initcalls();
lockup_detector_init();

+ page_alloc_init_late_prepare();
+
smp_init();
sched_init_smp();

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 752e5daf0896..cfa7175ff093 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1115,6 +1115,13 @@ static int __init set_buf_size(char *str)
if (buf_size == 0)
return 0;
trace_buf_size = buf_size;
+
+ /*
+ * The size of buffers are unpredictable so initialise all memory
+ * before the allocation attempt occurs.
+ */
+ disable_deferred_meminit();
+
return 1;
}
__setup("trace_buf_size=", set_buf_size);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 77e4d3c5c57b..4dd0e153b0f2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -290,6 +290,19 @@ EXPORT_SYMBOL(nr_online_nodes);
int page_group_by_mobility_disabled __read_mostly;

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+bool __initdata deferred_meminit_disabled;
+
+/*
+ * Allow deferred meminit to be disabled by subsystems that require large
+ * allocations before the memory allocator is fully initialised. It should
+ * only be used in cases where the size of the allocation may not fit into
+ * the 2G per node that is allocated serially.
+ */
+void __init disable_deferred_meminit(void)
+{
+ deferred_meminit_disabled = true;
+}
+
static inline void reset_deferred_meminit(pg_data_t *pgdat)
{
unsigned long max_initialise;
@@ -1567,6 +1580,23 @@ static int __init deferred_init_memmap(void *data)
}
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */

+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+/*
+ * Serialised init of remaining memory if large buffers of unknown size
+ * are required that might fail before parallelised meminit can start
+ */
+void __init page_alloc_init_late_prepare(void)
+{
+ int nid;
+
+ if (!deferred_meminit_disabled)
+ return;
+
+ for_each_node_state(nid, N_MEMORY)
+ deferred_init_memmap(NODE_DATA(nid));
+}
+#endif
+
void __init page_alloc_init_late(void)
{
struct zone *zone;
--
Mel Gorman
SUSE Labs

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