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Re: [PATCH] xen: Swap order of actions in the FREE*() macros
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 2 Feb 2024 07:57:14 +0100
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- Cc: George Dunlap <George.Dunlap@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 02 Feb 2024 06:57:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.02.2024 01:39, Andrew Cooper wrote:
> Wherever possible, it is a good idea to NULL out the visible reference to an
> object prior to freeing it. The FREE*() macros already collect together both
> parts, making it easy to adjust.
>
> This has a marginal code generation improvement, as some of the calls to the
> free() function can be tailcall optimised.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
However, ...
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -92,8 +92,9 @@ bool scrub_free_pages(void);
>
> /* Free an allocation, and zero the pointer to it. */
> #define FREE_XENHEAP_PAGES(p, o) do { \
> - free_xenheap_pages(p, o); \
> + void *_ptr_ = (p); \
... why a trailing _and_ a leading underscore? Sooner or later we'll
need to get rid of the leading ones anyway aiui (for Misra), here
and elsewhere. With it omitted right away (also below):
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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