Re: [PATCH RFC 3/4] mm/page_alloc_test: Add logic to isolate a node for testing

On Mon, Feb 24, 2025 at 02:47:13PM +0000, Brendan Jackman wrote:

In order to test the page allocator, we need an "instance" of the page allocator that is not subject to unpredictable perturbation by the live system. The closest thing that we have to an "instance" of the allocator is a NUMA node.

So, introduce a new concept of an "isolated" node. This is an extension of the existing concept of a "fake" node, with the addition that nothing else in the system will touch it unless instructed to by the test code.

The node is created during boot but has no memory nor any CPUs attached. It is not on any other node's fallback lists. Any code that pays general attention to NODE_DATA in such a way that might cause the page allocator data structures to be modified asynchronously to the test, is enlightened to ignore it via the node_isolated() helper.

Then, during initialization of the allocator test suite, hotplug out some memory and then plug it back in to the isolated node. The node can then be used for testing.

Because it's easy to miss code that needs enlightenment, which can lead to confusing test behaviour, also add some defensive checks to try and interference with the isolated node before the start of the test.

Signed-off-by: Brendan Jackman jackmanb@google.com

drivers/base/memory.c | 5 +- include/linux/memory.h | 4 ++ include/linux/nodemask.h | 13 +++++ kernel/kthread.c | 3 + mm/.kunitconfig | 10 +++- mm/Kconfig | 2 +- mm/internal.h | 11 ++++ mm/memory_hotplug.c | 26 ++++++--- mm/numa_memblks.c | 22 ++++++++ mm/page_alloc.c | 37 +++++++++++- mm/page_alloc_test.c | 142 ++++++++++++++++++++++++++++++++++++++++++++++- 11 files changed, 260 insertions(+), 15 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c index 348c5dbbfa68ad30d34b344ace1dd8deac0e1947..cdb893d7f13324862ee0943df080440d19fbd957 100644 --- a/drivers/base/memory.c +++ b/drivers/base/memory.c @@ -26,6 +26,8 @@ #include <linux/atomic.h> #include <linux/uaccess.h> +#include <kunit/visibility.h>

#define MEMORY_CLASS_NAME "memory" static const char *const online_type_to_str[] = { @@ -183,7 +185,7 @@ static inline unsigned long memblk_nr_poison(struct memory_block *mem) /*

• Must acquire mem_hotplug_lock in write mode.

*/ -static int memory_block_online(struct memory_block *mem) +VISIBLE_IF_KUNIT int memory_block_online(struct memory_block *mem) { unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr); unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block; @@ -250,6 +252,7 @@ static int memory_block_online(struct memory_block *mem) mem_hotplug_done(); return ret; } +EXPORT_SYMBOL_IF_KUNIT(memory_block_online); /*

• Must acquire mem_hotplug_lock in write mode.

diff --git a/include/linux/memory.h b/include/linux/memory.h index c0afee5d126ef65d420770e1f8669842c499c8de..99139a6e9c11a407a8d7bfb17b7bbe3d276048ff 100644 --- a/include/linux/memory.h +++ b/include/linux/memory.h @@ -177,6 +177,10 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func, register_memory_notifier(&fn##_mem_nb); \ }) +#ifdef CONFIG_KUNIT

Why not CONFIG_PAGE_ALLOC_KUNIT_TEST?

+int memory_block_online(struct memory_block *mem); +#endif

#ifdef CONFIG_NUMA void memory_block_add_nid(struct memory_block *mem, int nid, enum meminit_context context); diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h index 9fd7a0ce9c1a7336df46f12622867e6786a5c0a9..6ea38963487e1fbb800eab69e5e6413aa17a8047 100644 --- a/include/linux/nodemask.h +++ b/include/linux/nodemask.h @@ -536,6 +536,19 @@ static __always_inline int node_random(const nodemask_t *maskp) #define for_each_node(node) for_each_node_state(node, N_POSSIBLE) #define for_each_online_node(node) for_each_node_state(node, N_ONLINE)

+#ifdef CONFIG_PAGE_ALLOC_KUNIT_TEST +/*

• • An isolated node is a fake node for testing, that boots with no memory and no
• • attached CPUs, and nothing should touch it except for test code.
• */

+extern bool node_isolated(int node); +/* Only one isolated node is supported at present and it cannot be un-isolated. */ +extern void node_set_isolated(int node); +#else +static inline bool node_isolated(int node) { return false; } +#endif /* CONFIG_PAGE_ALLOC_KUNIT_TEST */

/*

• For nodemask scratch area.
• NODEMASK_ALLOC(type, name) allocates an object with a specified type and

diff --git a/kernel/kthread.c b/kernel/kthread.c index 5dc5b0d7238e85ad4074076e4036062c7bfcae74..93f65c5935cba8a59c7d3df2e36335130c3e1f71 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -9,6 +9,7 @@ */ #include <uapi/linux/sched/types.h> #include <linux/mm.h> +#include <linux/mmdebug.h> #include <linux/mmu_context.h> #include <linux/sched.h> #include <linux/sched/mm.h> @@ -511,6 +512,8 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), struct kthread_create_info *create = kmalloc(sizeof(*create), GFP_KERNEL);

• VM_WARN_ON(node != NUMA_NO_NODE && node_isolated(node));
• if (!create) return ERR_PTR(-ENOMEM); create->threadfn = threadfn;

diff --git a/mm/.kunitconfig b/mm/.kunitconfig index fcc28557fa1c1412b21f9dbddbf6a63adca6f2b4..4ff4e1654c3e9b364072d33bfffb3a2336825859 100644 --- a/mm/.kunitconfig +++ b/mm/.kunitconfig @@ -1,2 +1,10 @@ CONFIG_KUNIT=y -CONFIG_PAGE_ALLOC_KUNIT_TEST=y \ No newline at end of file +CONFIG_PAGE_ALLOC_KUNIT_TEST=y

+# Required for NUMA +CONFIG_SMP=y +# Used by tests to carve out fake node for isolating page_alloc data. +CONFIG_NUMA=y +CONFIG_NUMA_EMU=y +CONFIG_MEMORY_HOTPLUG=y +CONFIG_MEMORY_HOTREMOVE=y \ No newline at end of file diff --git a/mm/Kconfig b/mm/Kconfig index 1fac51c536c66243a1321195a78eb40668386158..64c3794120002a839f56e3feb284c6d5c2635f40 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1360,7 +1360,7 @@ config PT_RECLAIM config PAGE_ALLOC_KUNIT_TEST tristate "KUnit test for page allocator" if !KUNIT_ALL_TESTS

• depends on KUNIT

• depends on KUNIT && NUMA && MEMORY_HOTREMOVE default KUNIT_ALL_TESTS help Builds unit tests for page allocator.

diff --git a/mm/internal.h b/mm/internal.h index 109ef30fee11f8b399f6bac42eab078cd51e01a5..9dbe5853b90b53ff261ba1b2fca12eabfda1a9de 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1545,5 +1545,16 @@ static inline bool reclaim_pt_is_enabled(unsigned long start, unsigned long end, } #endif /* CONFIG_PT_RECLAIM */ +#ifdef CONFIG_PAGE_ALLOC_KUNIT_TEST +/*

• • Note that node_isolated() is separate, that's a "public API". But only
• • test code needs to look up which node is isolated.
• */

+extern int isolated_node; +#endif

+#ifdef CONFIG_KUNIT

Same here, why not just put it in the above #ifdef?

+void drain_pages(unsigned int cpu); +#endif #endif /* __MM_INTERNAL_H */ diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index e3655f07dd6e33efb3e811cab07f240649487441..968c23b6f347cf6a0c30d00cb556166b8df9c9c3 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1198,10 +1198,12 @@ int online_pages(unsigned long pfn, unsigned long nr_pages, arg.nr_pages = nr_pages; node_states_check_changes_online(nr_pages, zone, &arg);

• ret = memory_notify(MEM_GOING_ONLINE, &arg);
• ret = notifier_to_errno(ret);
• if (ret)

• goto failed_addition;
  

• if (!node_isolated(nid)) {

• ret = memory_notify(MEM_GOING_ONLINE, &arg);
  

• ret = notifier_to_errno(ret);
  

• if (ret)
  

• 	goto failed_addition;
  

• }

/* * Fixup the number of isolated pageblocks before marking the sections @@ -1242,19 +1244,27 @@ int online_pages(unsigned long pfn, unsigned long nr_pages, /* reinitialise watermarks and update pcp limits */ init_per_zone_wmark_min();

• kswapd_run(nid);
• kcompactd_run(nid);

• /*

• * Don't run daemons on the special test node, if that needs to be
  

• * tested the test should run it.
  

• */
  

• if (!node_isolated(nid)) {

• kswapd_run(nid);
  

• kcompactd_run(nid);
  

• }

writeback_set_ratelimit();

• memory_notify(MEM_ONLINE, &arg);

• if (!node_isolated(nid))

• memory_notify(MEM_ONLINE, &arg);
  

I am not familiar with this code, I am wondering if we can move things around to have a single block of things we skip for isolated nodes. It depends on ordering dependencies so we need someone who knows this code to tell us.

return 0; failed_addition: pr_debug("online_pages [mem %#010llx-%#010llx] failed\n", (unsigned long long) pfn << PAGE_SHIFT, (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);

• memory_notify(MEM_CANCEL_ONLINE, &arg);

• if (!node_isolated(nid))

• memory_notify(MEM_CANCEL_ONLINE, &arg);
  

  remove_pfn_range_from_zone(zone, pfn, nr_pages); return ret;

}

[..]

-static struct kunit_suite test_suite = { +struct kunit_suite page_alloc_test_suite = {

We should probably just intrdouce the suite as page_alloc_test_suite to begin with?

.name = "page_alloc", .test_cases = test_cases,

• .suite_init = populate_isolated_node,
• .suite_exit = depopulate_isolated_node,
• .init = test_init,

}; -kunit_test_suite(test_suite); +kunit_test_suite(page_alloc_test_suite); MODULE_LICENSE("GPL"); MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");

-- 2.48.1.601.g30ceb7b040-goog