Why do flush page cache twice when change TT's cache attribute

[Scott Fang]

In function ttm_tt_set_caching
,,,,,,,

    if (ttm->caching_state == tt_cached)
        drm_clflush_pages(ttm->pages, ttm->num_pages);

    for (i = 0; i < ttm->num_pages; ++i) {
        cur_page = ttm->pages[i];
        if (likely(cur_page != NULL)) {
            ret = ttm_tt_set_page_caching(cur_page,
                              ttm->caching_state,
                              c_state);
            if (unlikely(ret != 0))
                goto out_err;
        }
    }

    ttm->caching_state = c_state;

    return 0;


drm_clflush_pages flush cache one time.
then in the following function
ttm_tt_set_page_caching->set_memory_wc->change_page_attr_set:
in this function may flush page cache again.

Does the code do some abundant flush, or there is some trick to these codes?

Thanks for the answer in advance.

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