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Date: Thu, 29 Oct 2020 17:27:18 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
David Hildenbrand <david@...hat.com>,
Michal Hocko <mhocko@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Rashmica Gupta <rashmica.g@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Rapoport <rppt@...nel.org>,
Michal Hocko <mhocko@...e.com>,
Oscar Salvador <osalvador@...e.de>,
Wei Yang <richard.weiyang@...ux.alibaba.com>
Subject: [PATCH v1 4/4] powernv/memtrace: don't abuse memory hot(un)plug infrastructure for memory allocations
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@redhat.com
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.
Simple test under QEMU TCG (10GB RAM, single NUMA node):
sh-5.0# mount -t debugfs none /sys/kernel/debug/
sh-5.0# cat /sys/devices/system/memory/block_size_bytes
40000000
sh-5.0# echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 71.052836][ T356] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
sh-5.0# echo 0x80000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 75.424302][ T356] radix-mmu: Mapped 0x0000000080000000-0x00000000c0000000 with 64.0 KiB pages
[ 75.430549][ T356] memtrace: Freed trace memory back on node 0
[ 75.604520][ T356] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
sh-5.0# echo 0x100000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 80.418835][ T356] radix-mmu: Mapped 0x0000000080000000-0x0000000100000000 with 64.0 KiB pages
[ 80.430493][ T356] memtrace: Freed trace memory back on node 0
[ 80.433882][ T356] memtrace: Failed to allocate trace memory on node 0
sh-5.0# echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 91.920158][ T356] memtrace: Allocated trace memory on node 0 at 0x0000000080000000
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. I'm not able to come up with a better guess (most
probably, doing it on a section basis could be possible).
Suggested-by: Michal Hocko <mhocko@...nel.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Rashmica Gupta <rashmica.g@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Rapoport <rppt@...nel.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
arch/powerpc/platforms/powernv/Kconfig | 8 +-
arch/powerpc/platforms/powernv/memtrace.c | 134 ++++++++--------------
2 files changed, 49 insertions(+), 93 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 6828108486f8..8f47797a78c2 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -50,83 +50,50 @@ 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;
-}
-
-/* called with device_hotplug_lock held */
-static bool memtrace_offline_pages(u32 nid, u64 start_pfn, u64 nr_pages)
+static u64 memtrace_alloc_node(u32 nid, u64 size)
{
- const unsigned long start = PFN_PHYS(start_pfn);
- const unsigned long size = PFN_PHYS(nr_pages);
+ const unsigned long nr_pages = PHYS_PFN(size);
+ unsigned long pfn, start_pfn;
+ struct page *page;
- 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;
- }
+ /*
+ * Trace memory needs to be aligned to the size, which is guaranteed
+ * by alloc_contig_pages().
+ */
+ page = alloc_contig_pages(nr_pages, __GFP_THISNODE | __GFP_NOWARN,
+ nid, NULL);
+ if (!page)
+ return 0;
- walk_memory_blocks(start, size, (void *)MEM_OFFLINE,
- change_memblock_state);
+ /*
+ * Set pages PageOffline(), to indicate that nobody (e.g., hibernation,
+ * dumping, ...) should be touching these pages.
+ */
+ start_pfn = page_to_pfn(page);
+ 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 true;
+ return PFN_PHYS(start_pfn);
}
-static u64 memtrace_alloc_node(u32 nid, u64 size)
+static int memtrace_free(int nid, u64 start, u64 size)
{
- u64 start_pfn, end_pfn, nr_pages, pfn;
- u64 base_pfn;
- u64 bytes = memory_block_size_bytes();
+ 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;
- if (!node_spanned_pages(nid))
- return 0;
+ ret = arch_create_linear_mapping(nid, start, size, ¶ms);
+ if (ret)
+ return ret;
- 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) {
- /*
- * 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();
+ for (pfn = start_pfn; pfn < start_pfn + nr_pages; pfn++)
+ __ClearPageOffline(pfn_to_page(pfn));
+ free_contig_range(start_pfn, nr_pages);
return 0;
}
@@ -197,16 +164,11 @@ static int memtrace_init_debugfs(void)
return ret;
}
-static int online_mem_block(struct memory_block *mem, void *arg)
-{
- return device_online(&mem->dev);
-}
-
/*
- * 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;
@@ -214,7 +176,7 @@ 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;
@@ -224,30 +186,25 @@ 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;
@@ -269,16 +226,15 @@ static int memtrace_enable_set(void *data, u64 val)
return -EINVAL;
}
- /* Re-add/online previously removed/offlined memory */
+ /* Free all previously allocated memory. */
if (memtrace_size) {
- if (memtrace_online())
+ if (memtrace_free_regions())
return -EAGAIN;
}
if (!val)
return 0;
- /* Offline and remove memory */
if (memtrace_init_regions_runtime(val))
return -EINVAL;
--
2.26.2
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