Re: [Xen-devel] [PATCH 13/16] tmem: cleanup: __tmem_alloc_page: drop unneed parameters

[Bob Liu <bob.liu@xxxxxxxxxx>]

On 11/23/2013 02:17 AM, Konrad Rzeszutek Wilk wrote:
> On Wed, Nov 20, 2013 at 04:46:22PM +0800, Bob Liu wrote:
>> The two parameters of __tmem_alloc_page() can be reduced.
> 
> That is dangerous. The last one (no_heap) was added to guard
> against recursion. Check how tmem_alloc_page_thispool calls
> alloc_domheap_pages, whcih calls alloc_heap_pages which
> can call tmem_relinquish_pages, which can .. well, you will
> get the idea.
> 
>> tmem_called_from_tmem() was also dropped by this patch.
>>
>> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
>> ---
>>  xen/common/tmem.c          |   13 +++++--------
>>  xen/include/xen/tmem_xen.h |   11 +++++------
>>  2 files changed, 10 insertions(+), 14 deletions(-)
>>
>> diff --git a/xen/common/tmem.c b/xen/common/tmem.c
>> index ee61899..bf0fa1b 100644
>> --- a/xen/common/tmem.c
>> +++ b/xen/common/tmem.c
>> @@ -245,7 +245,7 @@ static struct page_info *tmem_alloc_page(struct 
>> tmem_pool *pool)
>>      if ( pool != NULL && is_persistent(pool) )
>>          pfp = __tmem_alloc_page_thispool(pool->client->domain);
>>      else
>> -        pfp = __tmem_alloc_page(pool,0);
>> +        pfp = __tmem_alloc_page();
>>      return pfp;
>>  }
>>  
>> @@ -263,9 +263,8 @@ static noinline void *tmem_mempool_page_get(unsigned 
>> long size)
>>      struct page_info *pi;
>>  
>>      ASSERT(size == PAGE_SIZE);
>> -    if ( (pi = __tmem_alloc_page(NULL,0)) == NULL )
>> +    if ( (pi = __tmem_alloc_page()) == NULL )
>>          return NULL;
>> -    ASSERT(IS_VALID_PAGE(pi));
>>      return page_to_virt(pi);
>>  }
>>  
>> @@ -2450,7 +2449,6 @@ void tmem_freeze_all(unsigned char key)
>>  void *tmem_relinquish_pages(unsigned int order, unsigned int memflags)
>>  {
>>      struct page_info *pfp;
>> -    unsigned long evicts_per_relinq = 0;
>>      int max_evictions = 10;
>>  
>>      if (!tmem_enabled() || !tmem_freeable_pages())
>> @@ -2464,14 +2462,13 @@ void *tmem_relinquish_pages(unsigned int order, 
>> unsigned int memflags)
>>          return NULL;
>>      }
>>  
>> -    if ( tmem_called_from_tmem(memflags) )
>> +    if ( memflags & MEMF_tmem )
>>          read_lock(&tmem_rwlock);
>>  
>> -    while ( (pfp = __tmem_alloc_page(NULL,1)) == NULL )
>> +    while ( (pfp = tmem_page_list_get()) == NULL )
> 
> No no. That could lead to bad recursion. You need to pass '1' somehow.
> 

I don't think so.
If pass '1' to __tmem_alloc_page(), __tmem_alloc_page() only call
tmem_page_list_get() and return.
It's no difference, so an extra parameter is unneeded.

> 
>>      {
>>          if ( (max_evictions-- <= 0) || !tmem_evict())
>>              break;
>> -        evicts_per_relinq++;
> 
> 
> ? Should this be a seperate patch?
> 
>>      }
>>      if ( pfp != NULL )
>>      {
>> @@ -2479,7 +2476,7 @@ void *tmem_relinquish_pages(unsigned int order, 
>> unsigned int memflags)
>>              scrub_one_page(pfp);
>>      }
>>  
>> -    if ( tmem_called_from_tmem(memflags) )
>> +    if ( memflags & MEMF_tmem )
> 
> Perhaps a comment too? /* Called recursively from within tmem. */
> 
>>          read_unlock(&tmem_rwlock);
>>  
>>      return pfp;
>> diff --git a/xen/include/xen/tmem_xen.h b/xen/include/xen/tmem_xen.h
>> index 7468c28..c4b9f5a 100644
>> --- a/xen/include/xen/tmem_xen.h
>> +++ b/xen/include/xen/tmem_xen.h
>> @@ -144,15 +144,16 @@ static inline void __tmem_free_page_thispool(struct 
>> page_info *pi)
>>  /*
>>   * Memory allocation for ephemeral (non-persistent) data
>>   */
>> -static inline struct page_info *__tmem_alloc_page(void *pool, int no_heap)
>> +static inline struct page_info *__tmem_alloc_page(void)
>>  {
>>      struct page_info *pi = tmem_page_list_get();
>>  
>> -    if ( pi == NULL && !no_heap )
>> +    if ( pi == NULL)
>>          pi = alloc_domheap_pages(0,0,MEMF_tmem);
>> -    ASSERT((pi == NULL) || IS_VALID_PAGE(pi));
>> -    if ( pi != NULL && !no_heap )
>> +
>> +    if ( pi )
>>          atomic_inc(&freeable_page_count);
>> +    ASSERT((pi == NULL) || IS_VALID_PAGE(pi));
>>      return pi;
>>  }
>>  

See __tmem_alloc_page() implementation here.

-- 
Regards,
-Bob

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