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Re: [Qemu-devel] [PATCH 3/3] qcow2: reorder fields in Qcow2CachedTable t

From: Alberto Garcia
Subject: Re: [Qemu-devel] [PATCH 3/3] qcow2: reorder fields in Qcow2CachedTable to reduce padding
Date: Tue, 26 May 2015 18:20:33 +0200
User-agent: Notmuch/0.13.2 (http://notmuchmail.org) Emacs/23.2.1 (i486-pc-linux-gnu)

On Tue 26 May 2015 06:10:11 PM CEST, Max Reitz wrote:
> On 18.05.2015 18:48, Alberto Garcia wrote:
>> Changing the current ordering saves 8 bytes per cache entry in x86_64.
> Hm, not seven?

No, the size is 32 before the patch and 24 afterwards.

What you save is the 7 bytes of padding after 'dirty' and one of the
bytes after 'ref'.

>>   typedef struct Qcow2CachedTable {
>>       int64_t  offset;
>> -    bool     dirty;
>>       uint64_t lru_counter;
>>       int      ref;
>> +    bool     dirty;
>>   } Qcow2CachedTable;


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