[PATCH v2 8/8] powernv/memtrace: don't abuse memory hot(un)plug infrastructure for memory allocations
From: David Hildenbrand
Date: Wed Nov 11 2020 - 09:54:10 EST
Let's use alloc_contig_pages() for allocating memory and remove the
linear mapping manually via arch_remove_linear_mapping(). Mark all pages
PG_offline, such that they will definitely not get touched - e.g.,
when hibernating. When freeing memory, try to revert what we did.
The original idea was discussed in:
https://lkml.kernel.org/r/48340e96-7e6b-736f-9e23-d3111b915b6e@xxxxxxxxxx
This is similar to CONFIG_DEBUG_PAGEALLOC handling on other
architectures, whereby only single pages are unmapped from the linear
mapping. Let's mimic what memory hot(un)plug would do with the linear
mapping.
We now need MEMORY_HOTPLUG and CONTIG_ALLOC as dependencies. Add a TODO
that we want to use __GFP_ZERO for clearing once alloc_contig_pages()
understands that.
Tested with in QEMU/TCG with 10 GiB of main memory:
[root@localhost ~]# echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 105.903043][ T1080] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
[root@localhost ~]# echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 145.042493][ T1080] radix-mmu: Mapped 0x0000000080000000-0x00000000c0000000 with 64.0 KiB pages
[ 145.049019][ T1080] memtrace: Freed trace memory back on node 0
[ 145.333960][ T1080] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
[root@localhost ~]# echo 0x80000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 213.606916][ T1080] radix-mmu: Mapped 0x0000000080000000-0x00000000c0000000 with 64.0 KiB pages
[ 213.613855][ T1080] memtrace: Freed trace memory back on node 0
[ 214.185094][ T1080] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
[root@localhost ~]# echo 0x100000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 234.874872][ T1080] radix-mmu: Mapped 0x0000000080000000-0x0000000100000000 with 64.0 KiB pages
[ 234.886974][ T1080] memtrace: Freed trace memory back on node 0
[ 234.890153][ T1080] memtrace: Failed to allocate trace memory on node 0
[root@localhost ~]# echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 259.490196][ T1080] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
I also made sure allocated memory is properly zeroed.
Note 1: We currently won't be allocating from ZONE_MOVABLE - because our
pages are not movable. However, as we don't run with any memory
hot(un)plug mechanism around, we could make an exception to
increase the chance of allocations succeeding.
Note 2: PG_reserved isn't sufficient. E.g., kernel_page_present() used
along PG_reserved in hibernation code will always return "true"
on powerpc, resulting in the pages getting touched. It's too
generic - e.g., indicates boot allocations.
Note 3: For now, we keep using memory_block_size_bytes() as minimum
granularity.
Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Rashmica Gupta <rashmica.g@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
arch/powerpc/platforms/powernv/Kconfig | 8 +-
arch/powerpc/platforms/powernv/memtrace.c | 163 ++++++++--------------
2 files changed, 62 insertions(+), 109 deletions(-)
diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index 938803eab0ad..619b093a0657 100644
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/arch/powerpc/platforms/powernv/Kconfig
@@ -27,11 +27,11 @@ config OPAL_PRD
recovery diagnostics on OpenPower machines
config PPC_MEMTRACE
- bool "Enable removal of RAM from kernel mappings for tracing"
- depends on PPC_POWERNV && MEMORY_HOTREMOVE
+ bool "Enable runtime allocation of RAM for tracing"
+ depends on PPC_POWERNV && MEMORY_HOTPLUG && CONTIG_ALLOC
help
- Enabling this option allows for the removal of memory (RAM)
- from the kernel mappings to be used for hardware tracing.
+ Enabling this option allows for runtime allocation of memory (RAM)
+ for hardware tracing.
config PPC_VAS
bool "IBM Virtual Accelerator Switchboard (VAS)"
diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index 0e42fe2d7b6a..5fc9408bb0b3 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -51,33 +51,12 @@ static const struct file_operations memtrace_fops = {
.open = simple_open,
};
-static int check_memblock_online(struct memory_block *mem, void *arg)
-{
- if (mem->state != MEM_ONLINE)
- return -1;
-
- return 0;
-}
-
-static int change_memblock_state(struct memory_block *mem, void *arg)
-{
- unsigned long state = (unsigned long)arg;
-
- mem->state = state;
-
- return 0;
-}
-
static void memtrace_clear_range(unsigned long start_pfn,
unsigned long nr_pages)
{
unsigned long pfn;
- /*
- * As pages are offline, we cannot trust the memmap anymore. As HIGHMEM
- * does not apply, avoid passing around "struct page" and use
- * clear_page() instead directly.
- */
+ /* As HIGHMEM does not apply, use clear_page() directly. */
for (pfn = start_pfn; pfn < start_pfn + nr_pages; pfn++) {
if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
cond_resched();
@@ -85,72 +64,39 @@ static void memtrace_clear_range(unsigned long start_pfn,
}
}
-/* called with device_hotplug_lock held */
-static bool memtrace_offline_pages(u32 nid, u64 start_pfn, u64 nr_pages)
-{
- const unsigned long start = PFN_PHYS(start_pfn);
- const unsigned long size = PFN_PHYS(nr_pages);
-
- if (walk_memory_blocks(start, size, NULL, check_memblock_online))
- return false;
-
- walk_memory_blocks(start, size, (void *)MEM_GOING_OFFLINE,
- change_memblock_state);
-
- if (offline_pages(start_pfn, nr_pages)) {
- walk_memory_blocks(start, size, (void *)MEM_ONLINE,
- change_memblock_state);
- return false;
- }
-
- walk_memory_blocks(start, size, (void *)MEM_OFFLINE,
- change_memblock_state);
-
-
- return true;
-}
-
static u64 memtrace_alloc_node(u32 nid, u64 size)
{
- u64 start_pfn, end_pfn, nr_pages, pfn;
- u64 base_pfn;
- u64 bytes = memory_block_size_bytes();
+ const unsigned long nr_pages = PHYS_PFN(size);
+ unsigned long pfn, start_pfn;
+ struct page *page;
- if (!node_spanned_pages(nid))
+ /*
+ * Trace memory needs to be aligned to the size, which is guaranteed
+ * by alloc_contig_pages().
+ */
+ page = alloc_contig_pages(nr_pages, GFP_KERNEL | __GFP_THISNODE |
+ __GFP_NOWARN, nid, NULL);
+ if (!page)
return 0;
+ start_pfn = page_to_pfn(page);
- start_pfn = node_start_pfn(nid);
- end_pfn = node_end_pfn(nid);
- nr_pages = size >> PAGE_SHIFT;
-
- /* Trace memory needs to be aligned to the size */
- end_pfn = round_down(end_pfn - nr_pages, nr_pages);
-
- lock_device_hotplug();
- for (base_pfn = end_pfn; base_pfn > start_pfn; base_pfn -= nr_pages) {
- if (memtrace_offline_pages(nid, base_pfn, nr_pages) == true) {
- /*
- * Clear the range while we still have a linear
- * mapping.
- */
- memtrace_clear_range(base_pfn, nr_pages);
- /*
- * Remove memory in memory block size chunks so that
- * iomem resources are always split to the same size and
- * we never try to remove memory that spans two iomem
- * resources.
- */
- end_pfn = base_pfn + nr_pages;
- for (pfn = base_pfn; pfn < end_pfn; pfn += bytes>> PAGE_SHIFT) {
- __remove_memory(nid, pfn << PAGE_SHIFT, bytes);
- }
- unlock_device_hotplug();
- return base_pfn << PAGE_SHIFT;
- }
- }
- unlock_device_hotplug();
+ /*
+ * Clear the range while we still have a linear mapping.
+ *
+ * TODO: use __GFP_ZERO with alloc_contig_pages() once supported.
+ */
+ memtrace_clear_range(start_pfn, nr_pages);
- return 0;
+ /*
+ * Set pages PageOffline(), to indicate that nobody (e.g., hibernation,
+ * dumping, ...) should be touching these pages.
+ */
+ for (pfn = start_pfn; pfn < start_pfn + nr_pages; pfn++)
+ __SetPageOffline(pfn_to_page(pfn));
+
+ arch_remove_linear_mapping(PFN_PHYS(start_pfn), size);
+
+ return PFN_PHYS(start_pfn);
}
static int memtrace_init_regions_runtime(u64 size)
@@ -220,16 +166,30 @@ static int memtrace_init_debugfs(void)
return ret;
}
-static int online_mem_block(struct memory_block *mem, void *arg)
+static int memtrace_free(int nid, u64 start, u64 size)
{
- return device_online(&mem->dev);
+ struct mhp_params params = { .pgprot = PAGE_KERNEL };
+ const unsigned long nr_pages = PHYS_PFN(size);
+ const unsigned long start_pfn = PHYS_PFN(start);
+ unsigned long pfn;
+ int ret;
+
+ ret = arch_create_linear_mapping(nid, start, size, ¶ms);
+ if (ret)
+ return ret;
+
+ for (pfn = start_pfn; pfn < start_pfn + nr_pages; pfn++)
+ __ClearPageOffline(pfn_to_page(pfn));
+
+ free_contig_range(start_pfn, nr_pages);
+ return 0;
}
/*
- * Iterate through the chunks of memory we have removed from the kernel
- * and attempt to add them back to the kernel.
+ * Iterate through the chunks of memory we allocated and attempt to expose
+ * them back to the kernel.
*/
-static int memtrace_online(void)
+static int memtrace_free_regions(void)
{
int i, ret = 0;
struct memtrace_entry *ent;
@@ -237,7 +197,7 @@ static int memtrace_online(void)
for (i = memtrace_array_nr - 1; i >= 0; i--) {
ent = &memtrace_array[i];
- /* We have onlined this chunk previously */
+ /* We have freed this chunk previously */
if (ent->nid == NUMA_NO_NODE)
continue;
@@ -247,30 +207,25 @@ static int memtrace_online(void)
ent->mem = 0;
}
- if (add_memory(ent->nid, ent->start, ent->size, MHP_NONE)) {
- pr_err("Failed to add trace memory to node %d\n",
+ if (memtrace_free(ent->nid, ent->start, ent->size)) {
+ pr_err("Failed to free trace memory on node %d\n",
ent->nid);
ret += 1;
continue;
}
- lock_device_hotplug();
- walk_memory_blocks(ent->start, ent->size, NULL,
- online_mem_block);
- unlock_device_hotplug();
-
/*
- * Memory was added successfully so clean up references to it
- * so on reentry we can tell that this chunk was added.
+ * Memory was freed successfully so clean up references to it
+ * so on reentry we can tell that this chunk was freed.
*/
debugfs_remove_recursive(ent->dir);
- pr_info("Added trace memory back to node %d\n", ent->nid);
+ pr_info("Freed trace memory back on node %d\n", ent->nid);
ent->size = ent->start = ent->nid = NUMA_NO_NODE;
}
if (ret)
return ret;
- /* If all chunks of memory were added successfully, reset globals */
+ /* If all chunks of memory were freed successfully, reset globals */
kfree(memtrace_array);
memtrace_array = NULL;
memtrace_size = 0;
@@ -295,18 +250,16 @@ static int memtrace_enable_set(void *data, u64 val)
mutex_lock(&memtrace_mutex);
- /* Re-add/online previously removed/offlined memory */
- if (memtrace_size) {
- if (memtrace_online())
- goto out_unlock;
- }
+ /* Free all previously allocated memory. */
+ if (memtrace_size && memtrace_free_regions())
+ goto out_unlock;
if (!val) {
rc = 0;
goto out_unlock;
}
- /* Offline and remove memory */
+ /* Allocate memory. */
if (memtrace_init_regions_runtime(val))
goto out_unlock;
--
2.26.2