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SubjectRe: [PATCH v3] devres: Explicitly align datai[] to 64-bit
On Mon, Jul 09, 2018 at 04:49:25PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 09, 2018 at 02:33:26PM +0000, Alexey Brodkin wrote:
> > > In fact, since alloc_dr() uses kmalloc() to allocate the entire thing,
> > > it is impossible to guarantee a larger alignment than kmalloc does.
> >
> > Well but 4-bytes [which is critical for atomic64_t] should be much less
> > than a sane cache line length so above should work.
>
> AFAICT ARCH_KMALLOC_MINALIGN ends up being 4 on x86_32 (it doesn't
> define ARCH_DMA_MINALIGN and doesn't seem to otherwise override the
> thing).

Shouldn't that be 8? AFAICT, __alignof__(unsigned long long) is 8 on
x86_32:

----
[mark@lakrids:~]% cat test.c
#include <stdio.h>

#define PRINT_TYPE_INFO(t) \
printf("%10s %5d %5d\n", #t, sizeof(t), __alignof__(t))

int main(int argc, char *argv[])
{
printf("%10s %5s %5s\n", "TYPE", "SIZE", "ALIGN");
PRINT_TYPE_INFO(int);
PRINT_TYPE_INFO(long);
PRINT_TYPE_INFO(long long);

return 0;
}
[mark@lakrids:~]% gcc -m32 test.c -o test
[mark@lakrids:~]% ./test
TYPE SIZE ALIGN
int 4 4
long 4 4
long long 8 8
----

Mark.

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