Re: [PATCH 10/14] s390/sclp_cmd: Replace page allocator calls with kzalloc()

[sashiko-bot@kernel.org]

> _sclp_get_core_info(), do_chp_configure() and sclp_chp_read_info()
> allocate the SCCBs used to read the CPU information, to configure a
> channel path and to read the channel path information.
> 
> These buffers can be allocated with kmalloc() as there's nothing special
> about them to go directly to the page allocator.
> 
> kmalloc() provides a better API that does not require ugly casts and
> kfree() does not need to know the size of the freed object.
> 
> Performance difference between kmalloc() and __get_free_pages() is not
> measurable as both allocators take an object/page from a per-CPU list for
> fast path allocations.
> 
> For the slow path the performance is anyway determined by the amount of
> reclaim involved rather than by what allocator is used.
> 
> While on it, allocate only the amount of memory the SCCB actually
> requires in _sclp_get_core_info() rather than rounding it up to the next
> power of two. An SCCB must be page aligned and kmalloc() guarantees that
> the alignment of an allocation is at least its largest power of two
> divisor, so the extended SCCB is still page aligned.
> 
> Replace use of __get_free_pages() and get_zeroed_page() with kzalloc()
> and free_page[s]() with kfree().
> 
> Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Sashiko has reviewed this patch and found no issues.

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