[Mesa-dev] [PATCH] mesa: Remove the ralloc canary on release builds.

[Eric Anholt]

Kenneth Graunke <kenneth at whitecape.org> writes:

> On 11/22/2013 12:21 AM, Eric Anholt wrote:
>> The canary is basically just to give a better debugging message when you
>> ralloc_free() something that wasn't rallocated.  Reduces maximum memory
>> usage of apitrace replay of the dota2 demo by 60MB on my 64-bit system (so
>> half that on a real 32-bit dota2 environment).
>
> Really, half?  It's an unsigned...that's 4 bytes regardless of 64-bit
> vs. 32-bit.  I think this should be 60MB of savings, end of story.

Scalar types get aligned to their size, so since it's followed by a
pointer, there's 4 bytes of pad in between.

For anyone that hasn't seen this tool before, check out pahole from the
dwarves package.  Run it on a .o file you think might be sucking up a
bunch of memory, and see your structs like:

class fs_inst : public backend_instruction {
public:

        /* class backend_instruction <ancestor>; */      /*     0    32 */

        /* XXX last struct has 7 bytes of padding */

        class fs_reg              dst;                   /*    32    48 */
        /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */
        class fs_reg              src[3];                /*    80   144 */
        /* --- cacheline 3 boundary (192 bytes) was 32 bytes ago --- */
        bool                       saturate;             /*   224     1 */

        /* XXX 3 bytes hole, try to pack */

        int                        conditional_mod;      /*   228     4 */
        uint8_t                    flag_subreg;          /*   232     1 */

        /* XXX 3 bytes hole, try to pack */

        int                        mlen;                 /*   236     4 */
        int                        regs_written;         /*   240     4 */
        int                        base_mrf;             /*   244     4 */
        uint32_t                   texture_offset;       /*   248     4 */
        int                        sampler;              /*   252     4 */
        /* --- cacheline 4 boundary (256 bytes) --- */
        int                        target;               /*   256     4 */
        bool                       eot;                  /*   260     1 */
        bool                       header_present;       /*   261     1 */
        bool                       shadow_compare;       /*   262     1 */
        bool                       force_uncompressed;   /*   263     1 */
        bool                       force_sechalf;        /*   264     1 */
        bool                       force_writemask_all;  /*   265     1 */

...

        /* size: 288, cachelines: 5, members: 21 */
        /* sum members: 280, holes: 3, sum holes: 8 */
        /* paddings: 1, sum paddings: 7 */
        /* last cacheline: 32 bytes */
};
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