Re: [PATCH v9 03/10] mm: thp: Introduce multi-size THP sysfs interface

[David Hildenbrand <david@redhat.com>]

On 07.12.23 17:12, Ryan Roberts wrote:
> In preparation for adding support for anonymous multi-size THP,
> introduce new sysfs structure that will be used to control the new
> behaviours. A new directory is added under transparent_hugepage for each
> supported THP size, and contains an `enabled` file, which can be set to
> "inherit" (to inherit the global setting), "always", "madvise" or
> "never". For now, the kernel still only supports PMD-sized anonymous
> THP, so only 1 directory is populated.
> 
> The first half of the change converts transhuge_vma_suitable() and
> hugepage_vma_check() so that they take a bitfield of orders for which
> the user wants to determine support, and the functions filter out all
> the orders that can't be supported, given the current sysfs
> configuration and the VMA dimensions. The resulting functions are
> renamed to thp_vma_suitable_orders() and thp_vma_allowable_orders()
> respectively. Convenience functions that take a single, unencoded order
> and return a boolean are also defined as thp_vma_suitable_order() and
> thp_vma_allowable_order().
> 
> The second half of the change implements the new sysfs interface. It has
> been done so that each supported THP size has a `struct thpsize`, which
> describes the relevant metadata and is itself a kobject. This is pretty
> minimal for now, but should make it easy to add new per-thpsize files to
> the interface if needed in future (e.g. per-size defrag). Rather than
> keep the `enabled` state directly in the struct thpsize, I've elected to
> directly encode it into huge_anon_orders_[always|madvise|inherit]
> bitfields since this reduces the amount of work required in
> thp_vma_allowable_orders() which is called for every page fault.
> 
> See Documentation/admin-guide/mm/transhuge.rst, as modified by this
> commit, for details of how the new sysfs interface works.
> 
> Reviewed-by: Barry Song <v-songbaohua@oppo.com>
> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Tested-by: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---

[...]

> +
> +static ssize_t thpsize_enabled_store(struct kobject *kobj,
> +				     struct kobj_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	int order = to_thpsize(kobj)->order;
> +	ssize_t ret = count;
> +
> +	if (sysfs_streq(buf, "always")) {
> +		spin_lock(&huge_anon_orders_lock);
> +		clear_bit(order, &huge_anon_orders_inherit);
> +		clear_bit(order, &huge_anon_orders_madvise);
> +		set_bit(order, &huge_anon_orders_always);
> +		spin_unlock(&huge_anon_orders_lock);
> +	} else if (sysfs_streq(buf, "inherit")) {
> +		spin_lock(&huge_anon_orders_lock);
> +		clear_bit(order, &huge_anon_orders_always);
> +		clear_bit(order, &huge_anon_orders_madvise);
> +		set_bit(order, &huge_anon_orders_inherit);
> +		spin_unlock(&huge_anon_orders_lock);
> +	} else if (sysfs_streq(buf, "madvise")) {
> +		spin_lock(&huge_anon_orders_lock);
> +		clear_bit(order, &huge_anon_orders_always);
> +		clear_bit(order, &huge_anon_orders_inherit);
> +		set_bit(order, &huge_anon_orders_madvise);
> +		spin_unlock(&huge_anon_orders_lock);
> +	} else if (sysfs_streq(buf, "never")) {
> +		spin_lock(&huge_anon_orders_lock);
> +		clear_bit(order, &huge_anon_orders_always);
> +		clear_bit(order, &huge_anon_orders_inherit);
> +		clear_bit(order, &huge_anon_orders_madvise);
> +		spin_unlock(&huge_anon_orders_lock);

Why not perform lock/unlock only once in surrounding code? :)


Much better

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb