linux-kernel - Re: questions about ttm_page

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Date:	Thu, 22 Jul 2010 10:10:13 -0400
From:	Jerome Glisse <glisse@...edesktop.org>
To:	Dan Carpenter <error27@...il.com>, suokkos@...il.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: questions about ttm_page_alloc.c

On 07/22/2010 07:56 AM, Dan Carpenter wrote:
> On Mon, Jul 12, 2010 at 07:12:37PM -0400, Jerome Glisse wrote:
>> On 07/12/2010 06:39 PM, Dan Carpenter wrote:
>>>      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.
>>>
>
> Thanks for answering about the wb vs uncached, but I'm still confused why we use
> &p->lru in most places and p->lru.prev in this place.
>
> regards,
> dan carpenter
>

This is because it use __list_del to remove a whole part of the list.

/*
  * Delete a list entry by making the prev/next entries
  * point to each other.
  *
  * This is only for internal list manipulation where we know
  * the prev/next entries already!
  */
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
»·······next->prev = prev;
»·······prev->next = next;
}

Cheers,
Jerome
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