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Message-ID: <2e90cce3-7a75-4827-81f1-01d9641c1b75@redhat.com>
Date: Tue, 29 Oct 2024 13:39:43 +0100
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>, x86@...nel.org,
linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, linux-mm@...ck.org
Cc: linux-cxl@...ck.org, Jonathan.Cameron@...wei.com,
dan.j.williams@...el.com, rrichter@....com, Terry.Bowman@....com,
dave.jiang@...el.com, ira.weiny@...el.com, alison.schofield@...el.com,
dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
rafael@...nel.org, lenb@...nel.org, osalvador@...e.de,
gregkh@...uxfoundation.org, akpm@...ux-foundation.org, rppt@...nel.org
Subject: Re: [PATCH v3 1/3] memory: implement
memory_block_advise/probe_max_size
On 22.10.24 23:34, Gregory Price wrote:
> Hotplug memory sources may have opinions on what the memblock size
> should be - usually for alignment purposes. For example, CXL memory
> extents can be 256MB with a matching alignment. If this size/alignment
> is smaller than the block size, it can result in stranded capacity.
>
> Implement memory_block_advise_max_size for use prior to allocator init,
> for software to advise the system on the max block size.
>
> Implement memory_block_probe_max_size for use by arch init code to
> calculate the best block size. Use of advice is architecture defined.
>
> The probe value can never change after first probe. Calls to advise
> after probe will return -EBUSY to aid debugging.
>
> On systems without hotplug, always return -ENODEV and 0 respectively.
>
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
> drivers/base/memory.c | 43 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/memory.h | 10 ++++++++++
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 67858eeb92ed..a0fd9e1451aa 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -110,6 +110,49 @@ static void memory_block_release(struct device *dev)
> kfree(mem);
> }
>
> +/*
As Mike says, this documentation looks incomplete.
/**
* memory_block_advise_max_size: suggest a maximum memory block size
...
> + * @size: suggestion for maximum block size. must be aligned on power of 2.
> + *
> + * Early boot software (pre-allocator init) may advise archs on the max block
> + * size.This value can only decrease after initialization, as the intent is to
Missing space after "size."
> + * identify the largest supported alignment for all sources.
> + *
> + * Use of this value is arch dependent, as is min/max block size.
> + *
> + * Returns: 0 on success
> + * -EINVAL if size is 0 or not pow2 aligned
> + * -EBUSY if value has already been probed
> + */
> +static size_t memory_block_advised_sz;
> +static bool memory_block_size_probed;
> +int memory_block_advise_max_size(size_t bz)
> +{
> + if (!bz || (bz & (bz - 1)) != 0)
> + return -EINVAL;
> +
> + if (memory_block_size_probed)
> + return -EBUSY;
> +
> + if (memory_block_advised_sz)
> + memory_block_advised_sz = min(bz, memory_block_advised_sz);
> + else
> + memory_block_advised_sz = bz;
> +
> + return 0;
> +}
> +
> +/*
> + * memory_block_probe_max_size provides a suggested maximum memory block
> + * size value. After the first call, the value can never change.
> + *
> + * Returns: advised size in bytes, or 0 if never set.
> + */
> +size_t memory_block_probe_max_size(void)
Can we call that "memory_block_advised_max_size()" ?
> +{
> + memory_block_size_probed = true;
Call this "memory_block_advised_size_queried" ?
> + return memory_block_advised_sz;
> +}
--
Cheers,
David / dhildenb
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