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Date: Tue, 17 Oct 2023 14:33:57 +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 v6 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 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.
>
> This does preclude being able to use PUD mappings in the direct map; a
> proposal to how this could be optimized in the future is laid out
> here[1].
>
> [1]: https://lore.kernel.org/linux-mm/b6753402-2de9-25b2-36e9-eacd49752b19@redhat.com/
>
> 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>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> ---
> mm/memory_hotplug.c | 214 ++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 148 insertions(+), 66 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6be7de9efa55..83e5ec377aad 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1380,6 +1380,43 @@ 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 = kmemdup(&mhp_altmap, sizeof(struct vmem_altmap),
> + GFP_KERNEL);
> + if (!params.altmap)
> + return -ENOMEM;
> + }
> +
> + /* 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 +1425,10 @@ 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 +1469,21 @@ 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 = kmemdup(&mhp_altmap,
> - 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;
> }
> - /* 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);
IIUC, if (mhp_flags & MHP_MEMMAP_ON_MEMORY) == true and
mhp_supports_memmap_on_memory(memblock_size) == false, we will go here
and allocate params.altmap in add_memory_create_devices(). If so, it
seems better to pass whether to create altmap instead of mhp_flags to
add_memory_create_devices().
--
Best Regards,
Huang, Ying
> + if (ret)
> + goto error;
> }
>
> if (new_node) {
[snip]
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