zink: use a slab allocator for zink_kopper_present_info

this improves perf slightly at extremely high fps

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27867>

src/gallium/drivers/zink/zink_kopper.c

@@ -760,7 +760,7 @@ out:
       struct pipe_resource *pres = &cpi->res->base.b;
       pipe_resource_reference(&pres, NULL);
    }
-   free(cpi);
+   slab_free_st(&screen->present_mempool, cpi);
 }
 
 void
@@ -775,7 +775,7 @@ zink_kopper_present_queue(struct zink_screen *screen, struct zink_resource *res)
    if (cdt->swapchain->last_present != UINT32_MAX)
       prune_old_swapchains(screen, cdt, false);
 
-   struct zink_kopper_present_info *cpi = malloc(sizeof(struct zink_kopper_present_info));
+   struct zink_kopper_present_info *cpi = slab_alloc_st(&screen->present_mempool);
    if (!cpi) {
       mesa_loge("ZINK: failed to allocate cpi!");
       return;

src/gallium/drivers/zink/zink_screen.c

@@ -1619,6 +1619,7 @@ zink_destroy_screen(struct pipe_screen *pscreen)
       close(screen->drm_fd);
 
    slab_destroy_parent(&screen->transfer_pool);
+   slab_destroy(&screen->present_mempool);
    ralloc_free(screen);
    glsl_type_singleton_decref();
 }
@@ -3488,6 +3489,7 @@ zink_internal_create_screen(const struct pipe_screen_config *config, int64_t dev
    populate_format_props(screen);
 
    slab_create_parent(&screen->transfer_pool, sizeof(struct zink_transfer), 16);
+   slab_create(&screen->present_mempool, sizeof(struct zink_kopper_present_info), 16);
 
    screen->driconf.inline_uniforms = debug_get_bool_option("ZINK_INLINE_UNIFORMS", screen->is_cpu) && !(zink_debug & ZINK_DEBUG_DGC);
 

src/gallium/drivers/zink/zink_types.h

@@ -1434,6 +1434,7 @@ struct zink_screen {
    bool device_lost;
    int drm_fd;
 
+   struct slab_mempool present_mempool;
    struct slab_parent_pool transfer_pool;
    struct disk_cache *disk_cache;
    struct util_queue cache_put_thread;