linux-kernel - questions about ttm_page

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Message-ID: <20100712223905.GH5658@bicker>
Date:	Tue, 13 Jul 2010 00:39:05 +0200
From:	Dan Carpenter <error27@...il.com>
To:	suokkos@...il.com
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: questions about ttm_page_alloc.c

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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