Re: [Qemu-block] [PATCH] qcow2: do lazy allocation of the L2 cache

[Kevin Wolf]

Am 24.04.2015 um 11:26 hat Stefan Hajnoczi geschrieben:
> The posix_memalign() call wastes memory.  I compared:
> 
>   posix_memalign(&memptr, 65536, 2560 * 65536);
>   memset(memptr, 0, 2560 * 65536);
> 
> with:
> 
>   for (i = 0; i < 2560; i++) {
>       posix_memalign(&memptr, 65536, 65536);
>       memset(memptr, 0, 65536);
>   }

64k alignment is too much, in practice you need 512b or 4k, which
probably wastes a lot less memory.

But I just looked at the qcow2 cache code and you're right anyway.
Allocating one big block instead of many small allocations in a loop
looks like a good idea either way.

Kevin

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