Re: questions about ttm_page_alloc.c

[Jerome Glisse <glisse@freedesktop.org>]

On 07/12/2010 06:39 PM, Dan Carpenter wrote:
> I'm investigating: https://bugzilla.kernel.org/show_bug.cgi?id=16337
>
> He is using the new radeon with the new ttm pool wc/uc page allocator.
> I'm sort of over my head when it comes to mm stuff so forgive me if
> these are dumb questions...  I'm looking at
> drivers/gpu/drm/ttm/ttm_page_alloc.c.
>
>     230  static int set_pages_array_wc(struct page **pages, int addrinarray)
>     231  {
>     232  #ifdef TTM_HAS_AGP
>     233          int i;
>     234
>     235          for (i = 0; i<  addrinarray; i++)
>     236                  map_page_into_agp(pages[i]);
> 			^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> 	This actually sets the pages to uncached and not to write
> 	cached.  Is that deliberate?
>
>     237  #endif
>     238          return 0;
>     239  }
>
> [snip]
>
>     327                  pages_to_free[freed_pages++] = p;
>     328                  /* We can only remove NUM_PAGES_TO_ALLOC at a time. */
>     329                  if (freed_pages>= NUM_PAGES_TO_ALLOC) {
>     330                          /* remove range of pages from the pool */
>     331                          __list_del(p->lru.prev,&pool->list);
>
> 	Why do we use p->lru.prev here when we use&p->lru in other
> 	places?
>
>     332
>     333                          ttm_pool_update_free_locked(pool, freed_pages);
>     334                          /**
>     335                           * Because changing page caching is costly
>     336                           * we unlock the pool to prevent stalling.
>
> regards,
> dan carpenter
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No it's fine, this code is for non x86 CPU, and on such platform
we assume wc == uncached and wb is normal (ie cached).

Cheers,
Jerome