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Message-ID: <87a5vmadcw.fsf@linux.ibm.com>
Date: Sun, 23 Jul 2023 20:23:19 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To: Vishal Verma <vishal.l.verma@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>,
Oscar Salvador <osalvador@...e.de>,
Dan Williams <dan.j.williams@...el.com>,
Dave Jiang <dave.jiang@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
Huang Ying <ying.huang@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Jeff Moyer <jmoyer@...hat.com>,
Vishal Verma <vishal.l.verma@...el.com>
Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on_memory
requests across memblocks
Vishal Verma <vishal.l.verma@...el.com> writes:
> The MHP_MEMMAP_ON_MEMORY flag for hotplugged memory is currently
> restricted to 'memblock_size' chunks of memory being added. Adding a
> larger span of memory precludes memmap_on_memory semantics.
>
> For users of hotplug such as kmem, large amounts of memory might get
> added from the CXL subsystem. In some cases, this amount may exceed the
> available 'main memory' to store the memmap for the memory being added.
> In this case, it is useful to have a way to place the memmap on the
> memory being added, even if it means splitting the addition into
> memblock-sized chunks.
>
> Change add_memory_resource() to loop over memblock-sized chunks of
> memory if caller requested memmap_on_memory, and if other conditions for
> it are met,. Teach try_remove_memory() to also expect that a memory
> range being removed might have been split up into memblock sized chunks,
> and to loop through those as needed.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> ---
> mm/memory_hotplug.c | 154 +++++++++++++++++++++++++++++++---------------------
> 1 file changed, 91 insertions(+), 63 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e9bcacbcbae2..20456f0d28e6 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1286,6 +1286,35 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
> }
> EXPORT_SYMBOL_GPL(mhp_supports_memmap_on_memory);
>
> +static int add_memory_create_devices(int nid, struct memory_group *group,
> + u64 start, u64 size, mhp_t mhp_flags)
> +{
> + struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> + struct vmem_altmap mhp_altmap = {};
> + int ret;
> +
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY)) {
> + mhp_altmap.free = PHYS_PFN(size);
> + mhp_altmap.base_pfn = PHYS_PFN(start);
> + params.altmap = &mhp_altmap;
> + }
> +
> + /* call arch's memory hotadd */
> + ret = arch_add_memory(nid, start, size, ¶ms);
> + if (ret < 0)
> + return ret;
> +
> + /* create memory block devices after memory was added */
> + ret = create_memory_block_devices(start, size, mhp_altmap.alloc,
> + group);
> + if (ret) {
> + arch_remove_memory(start, size, NULL);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> /*
> * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> * and online/offline operations (triggered e.g. by sysfs).
> @@ -1294,11 +1323,10 @@ EXPORT_SYMBOL_GPL(mhp_supports_memmap_on_memory);
> */
> int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> {
> - struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> + unsigned long memblock_size = memory_block_size_bytes();
> enum memblock_flags memblock_flags = MEMBLOCK_NONE;
> - struct vmem_altmap mhp_altmap = {};
> struct memory_group *group = NULL;
> - u64 start, size;
> + u64 start, size, cur_start;
> bool new_node = false;
> int ret;
>
> @@ -1339,27 +1367,20 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> /*
> * Self hosted memmap array
> */
> - if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
> - if (!mhp_supports_memmap_on_memory(size)) {
> - ret = -EINVAL;
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
> + mhp_supports_memmap_on_memory(memblock_size)) {
> + for (cur_start = start; cur_start < start + size;
> + cur_start += memblock_size) {
> + ret = add_memory_create_devices(nid, group, cur_start,
> + memblock_size,
> + mhp_flags);
> + if (ret)
> + goto error;
> + }
We should handle the below error details here.
1) If we hit an error after some blocks got added, should we iterate over rest of the dev_dax->nr_range.
2) With some blocks added if we return a failure here, we remove the
resource in dax_kmem. Is that ok?
IMHO error handling with partial creation of memory blocks in a resource range should be
documented with this change.
> + } else {
> + ret = add_memory_create_devices(nid, group, start, size, mhp_flags);
> + if (ret)
> goto error;
> - }
> - mhp_altmap.free = PHYS_PFN(size);
> - mhp_altmap.base_pfn = PHYS_PFN(start);
> - params.altmap = &mhp_altmap;
> - }
> -
> - /* call arch's memory hotadd */
> - ret = arch_add_memory(nid, start, size, ¶ms);
> - if (ret < 0)
> - goto error;
> -
> - /* create memory block devices after memory was added */
> - ret = create_memory_block_devices(start, size, mhp_altmap.alloc,
> - group);
> - if (ret) {
> - arch_remove_memory(start, size, NULL);
> - goto error;
> }
>
> if (new_node) {
> @@ -2035,12 +2056,38 @@ void try_offline_node(int nid)
> }
> EXPORT_SYMBOL(try_offline_node);
>
> -static int __ref try_remove_memory(u64 start, u64 size)
> +static void __ref __try_remove_memory(int nid, u64 start, u64 size,
> + struct vmem_altmap *altmap)
> {
> - struct vmem_altmap mhp_altmap = {};
> - struct vmem_altmap *altmap = NULL;
> - unsigned long nr_vmemmap_pages;
> - int rc = 0, nid = NUMA_NO_NODE;
> + /* remove memmap entry */
> + firmware_map_remove(start, start + size, "System RAM");
> +
> + /*
> + * Memory block device removal under the device_hotplug_lock is
> + * a barrier against racing online attempts.
> + */
> + remove_memory_block_devices(start, size);
> +
> + mem_hotplug_begin();
> +
> + arch_remove_memory(start, size, altmap);
> +
> + if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> + memblock_phys_free(start, size);
> + memblock_remove(start, size);
> + }
> +
> + release_mem_region_adjustable(start, size);
> +
> + if (nid != NUMA_NO_NODE)
> + try_offline_node(nid);
> +
> + mem_hotplug_done();
> +}
> +
> +static int try_remove_memory(u64 start, u64 size)
> +{
> + int rc, nid = NUMA_NO_NODE;
>
> BUG_ON(check_hotplug_memory_range(start, size));
>
> @@ -2058,20 +2105,21 @@ static int __ref try_remove_memory(u64 start, u64 size)
> return rc;
>
> /*
> - * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
> - * the same granularity it was added - a single memory block.
> + * For memmap_on_memory, the altmaps could have been added on
> + * a per-memblock basis. Loop through the entire range if so,
> + * and remove each memblock and its altmap
> */
> if (mhp_memmap_on_memory()) {
> - nr_vmemmap_pages = walk_memory_blocks(start, size, NULL,
> - get_nr_vmemmap_pages_cb);
> - if (nr_vmemmap_pages) {
> - if (size != memory_block_size_bytes()) {
> - pr_warn("Refuse to remove %#llx - %#llx,"
> - "wrong granularity\n",
> - start, start + size);
> - return -EINVAL;
> - }
> + unsigned long memblock_size = memory_block_size_bytes();
> + struct vmem_altmap mhp_altmap = {};
> + struct vmem_altmap *altmap;
> + u64 cur_start;
>
> + for (cur_start = start; cur_start < start + size;
> + cur_start += memblock_size) {
> + unsigned long nr_vmemmap_pages =
> + walk_memory_blocks(start, memblock_size, NULL,
> + get_nr_vmemmap_pages_cb);
> /*
> * Let remove_pmd_table->free_hugepage_table do the
> * right thing if we used vmem_altmap when hot-adding
> @@ -2079,33 +2127,13 @@ static int __ref try_remove_memory(u64 start, u64 size)
> */
> mhp_altmap.alloc = nr_vmemmap_pages;
> altmap = &mhp_altmap;
> + __try_remove_memory(nid, cur_start, memblock_size,
> + altmap);
> }
> + } else {
> + __try_remove_memory(nid, start, size, NULL);
> }
>
> - /* remove memmap entry */
> - firmware_map_remove(start, start + size, "System RAM");
> -
> - /*
> - * Memory block device removal under the device_hotplug_lock is
> - * a barrier against racing online attempts.
> - */
> - remove_memory_block_devices(start, size);
> -
> - mem_hotplug_begin();
> -
> - arch_remove_memory(start, size, altmap);
> -
> - if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> - memblock_phys_free(start, size);
> - memblock_remove(start, size);
> - }
> -
> - release_mem_region_adjustable(start, size);
> -
> - if (nid != NUMA_NO_NODE)
> - try_offline_node(nid);
> -
> - mem_hotplug_done();
> return 0;
> }
>
>
> --
> 2.41.0
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