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Message-ID: <87jzrylslk.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Sat, 07 Oct 2023 16:55:19 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Vishal Verma <vishal.l.verma@...el.com>
Cc: 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>,
<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
<nvdimm@...ts.linux.dev>, <linux-cxl@...r.kernel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
Michal Hocko <mhocko@...e.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH v5 1/2] 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 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: Michal Hocko <mhocko@...e.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 | 162 ++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 99 insertions(+), 63 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index f8d3e7427e32..77ec6f15f943 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1380,6 +1380,44 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
> return arch_supports_memmap_on_memory(vmemmap_size);
> }
>
> +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 = {
> + .base_pfn = PHYS_PFN(start),
> + .end_pfn = PHYS_PFN(start + size - 1),
> + };
> + int ret;
> +
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY)) {
> + mhp_altmap.free = memory_block_memmap_on_memory_pages();
> + params.altmap = kmalloc(sizeof(struct vmem_altmap), GFP_KERNEL);
> + if (!params.altmap)
> + return -ENOMEM;
> +
> + memcpy(params.altmap, &mhp_altmap, sizeof(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, params.altmap, group);
> + if (ret)
> + goto err_bdev;
> +
> + return 0;
> +
> +err_bdev:
> + arch_remove_memory(start, size, NULL);
> +error:
> + kfree(params.altmap);
> + return ret;
> +}
> +
> /*
> * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> * and online/offline operations (triggered e.g. by sysfs).
> @@ -1388,14 +1426,10 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
> */
> 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 = {
> - .base_pfn = PHYS_PFN(res->start),
> - .end_pfn = PHYS_PFN(res->end),
> - };
> struct memory_group *group = NULL;
> - u64 start, size;
> + u64 start, size, cur_start;
> bool new_node = false;
> int ret;
>
> @@ -1436,28 +1470,21 @@ 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)) {
> - mhp_altmap.free = memory_block_memmap_on_memory_pages();
> - params.altmap = kmalloc(sizeof(struct vmem_altmap), GFP_KERNEL);
> - if (!params.altmap)
> + 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;
> -
> - memcpy(params.altmap, &mhp_altmap, sizeof(mhp_altmap));
> }
> - /* fallback to not using altmap */
> - }
> -
> - /* call arch's memory hotadd */
> - ret = arch_add_memory(nid, start, size, ¶ms);
> - if (ret < 0)
> - goto error_free;
> -
> - /* create memory block devices after memory was added */
> - ret = create_memory_block_devices(start, size, params.altmap, group);
> - if (ret) {
> - arch_remove_memory(start, size, NULL);
> - goto error_free;
> + } else {
> + ret = add_memory_create_devices(nid, group, start, size,
> + mhp_flags);
> + if (ret)
> + goto error;
> }
>
> if (new_node) {
> @@ -1494,8 +1521,6 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> walk_memory_blocks(start, size, NULL, online_memory_block);
>
> return ret;
> -error_free:
> - kfree(params.altmap);
> error:
> if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
> memblock_remove(start, size);
> @@ -2146,12 +2171,41 @@ void try_offline_node(int nid)
> }
> EXPORT_SYMBOL(try_offline_node);
>
> -static int __ref try_remove_memory(u64 start, u64 size)
> +static void __ref remove_memory_block_and_altmap(int nid, u64 start, u64 size)
> {
> + int rc = 0;
> struct memory_block *mem;
> - int rc = 0, nid = NUMA_NO_NODE;
> struct vmem_altmap *altmap = NULL;
>
> + rc = walk_memory_blocks(start, size, &mem, test_has_altmap_cb);
> + if (rc) {
> + altmap = mem->altmap;
> + /*
> + * Mark altmap NULL so that we can add a debug
> + * check on memblock free.
> + */
> + mem->altmap = NULL;
> + }
> +
> + /*
> + * Memory block device removal under the device_hotplug_lock is
> + * a barrier against racing online attempts.
> + */
> + remove_memory_block_devices(start, size);
> +
> + arch_remove_memory(start, size, altmap);
> +
> + /* Verify that all vmemmap pages have actually been freed. */
> + if (altmap) {
> + WARN(altmap->alloc, "Altmap not fully unmapped");
> + kfree(altmap);
> + }
> +}
> +
> +static int __ref try_remove_memory(u64 start, u64 size)
> +{
> + int rc, nid = NUMA_NO_NODE;
> +
> BUG_ON(check_hotplug_memory_range(start, size));
>
> /*
> @@ -2167,47 +2221,28 @@ static int __ref try_remove_memory(u64 start, u64 size)
> if (rc)
> return rc;
>
> + mem_hotplug_begin();
> +
> /*
> - * 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()) {
IIUC, even if mhp_memmap_on_memory() returns true, it's still possible
that the memmap is put in DRAM after [2/2]. So that,
arch_remove_memory() are called for each memory block unnecessarily. Can
we detect this (via altmap?) and call remove_memory_block_and_altmap()
for the whole range?
> - rc = walk_memory_blocks(start, size, &mem, test_has_altmap_cb);
> - if (rc) {
> - if (size != memory_block_size_bytes()) {
> - pr_warn("Refuse to remove %#llx - %#llx,"
> - "wrong granularity\n",
> - start, start + size);
> - return -EINVAL;
> - }
> - altmap = mem->altmap;
> - /*
> - * Mark altmap NULL so that we can add a debug
> - * check on memblock free.
> - */
> - mem->altmap = NULL;
> - }
> + unsigned long memblock_size = memory_block_size_bytes();
> + u64 cur_start;
> +
> + for (cur_start = start; cur_start < start + size;
> + cur_start += memblock_size)
> + remove_memory_block_and_altmap(nid, cur_start,
> + memblock_size);
> + } else {
> + remove_memory_block_and_altmap(nid, start, size);
> }
>
> /* 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);
> -
> - /* Verify that all vmemmap pages have actually been freed. */
> - if (altmap) {
> - WARN(altmap->alloc, "Altmap not fully unmapped");
> - kfree(altmap);
> - }
> -
> if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> memblock_phys_free(start, size);
> memblock_remove(start, size);
> @@ -2219,6 +2254,7 @@ static int __ref try_remove_memory(u64 start, u64 size)
> try_offline_node(nid);
>
> mem_hotplug_done();
> +
> return 0;
> }
--
Best Regards,
Huang, Ying
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