Re: [PATCH 7/8] pnfsblock: add im_extents to pnfs_inval_markings

[Benny Halevy <bhalevy@tonian.com>]

On 2011-11-10 10:54, Benny Halevy wrote:
> On 2011-11-09 17:16, Peng Tao wrote:
>> It stores a list of short extents for INVAL->RW conversion.
>> Also add two functions to manipulate them, in preparation to
>> move malloc logic out of end_io.
>>
>> Signed-off-by: Peng Tao <peng_tao@emc.com>
>> ---
>>  fs/nfs/blocklayout/blocklayout.c |    6 ++++++
>>  fs/nfs/blocklayout/blocklayout.h |    5 +++++
>>  fs/nfs/blocklayout/extents.c     |   37 +++++++++++++++++++++++++++++++++++++
>>  3 files changed, 48 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
>> index 815c0c3..cb4ff0f 100644
>> --- a/fs/nfs/blocklayout/blocklayout.c
>> +++ b/fs/nfs/blocklayout/blocklayout.c
>> @@ -706,11 +706,17 @@ static void
>>  release_inval_marks(struct pnfs_inval_markings *marks)
>>  {
>>  	struct pnfs_inval_tracking *pos, *temp;
>> +	struct pnfs_block_short_extent *se, *stemp;
>>  
>>  	list_for_each_entry_safe(pos, temp, &marks->im_tree.mtt_stub, it_link) {
>>  		list_del(&pos->it_link);
>>  		kfree(pos);
>>  	}
>> +
>> +	list_for_each_entry_safe(se, stemp, &marks->im_extents, bse_node) {
>> +		list_del(&se->bse_node);
>> +		kfree(se);
>> +	}
>>  	return;
>>  }
>>  
>> diff --git a/fs/nfs/blocklayout/blocklayout.h b/fs/nfs/blocklayout/blocklayout.h
>> index 60728ac..df0e0fb 100644
>> --- a/fs/nfs/blocklayout/blocklayout.h
>> +++ b/fs/nfs/blocklayout/blocklayout.h
>> @@ -70,6 +70,7 @@ struct pnfs_inval_markings {
>>  	spinlock_t	im_lock;
>>  	struct my_tree	im_tree;	/* Sectors that need LAYOUTCOMMIT */
>>  	sector_t	im_block_size;	/* Server blocksize in sectors */
>> +	struct list_head im_extents;	/* List of short extents for INVAL->RW conversion */
>>  };
>>  
>>  struct pnfs_inval_tracking {
>> @@ -105,6 +106,7 @@ BL_INIT_INVAL_MARKS(struct pnfs_inval_markings *marks, sector_t blocksize)
>>  {
>>  	spin_lock_init(&marks->im_lock);
>>  	INIT_LIST_HEAD(&marks->im_tree.mtt_stub);
>> +	INIT_LIST_HEAD(&marks->im_extents);
>>  	marks->im_block_size = blocksize;
>>  	marks->im_tree.mtt_step_size = min((sector_t)PAGE_CACHE_SECTORS,
>>  					   blocksize);
>> @@ -200,5 +202,8 @@ int bl_add_merge_extent(struct pnfs_block_layout *bl,
>>  			 struct pnfs_block_extent *new);
>>  int bl_mark_for_commit(struct pnfs_block_extent *be,
>>  			sector_t offset, sector_t length);
>> +int bl_push_one_short_extent(struct pnfs_inval_markings *marks);
>> +struct pnfs_block_short_extent*
>> +bl_pop_short_extent(struct pnfs_inval_markings *marks, int num_to_pop);
>>  
>>  #endif /* FS_NFS_NFS4BLOCKLAYOUT_H */
>> diff --git a/fs/nfs/blocklayout/extents.c b/fs/nfs/blocklayout/extents.c
>> index 952ea8a..72c7fa1 100644
>> --- a/fs/nfs/blocklayout/extents.c
>> +++ b/fs/nfs/blocklayout/extents.c
>> @@ -863,3 +863,40 @@ clean_pnfs_block_layoutupdate(struct pnfs_block_layout *bl,
>>  		}
>>  	}
>>  }
>> +
>> +int
>> +bl_push_one_short_extent(struct pnfs_inval_markings *marks) {
>> +	struct pnfs_block_short_extent *new;
>> +
>> +	new = kmalloc(sizeof(*new), GFP_NOFS);
>> +	if (unlikely(!new))
>> +		return -ENOMEM;
>> +
>> +	spin_lock(&marks->im_lock);
>> +	list_add(&new->bse_node, &marks->im_extents);
>> +	spin_unlock(&marks->im_lock);
>> +
>> +	return 0;
>> +}
>> +
>> +struct pnfs_block_short_extent*
>> +bl_pop_short_extent(struct pnfs_inval_markings *marks, int num_to_pop) {
>> +	struct pnfs_block_short_extent *rv = NULL;

The use case for bl_pop_short_extent comes only in the next patch
so it should be introduced there in principle, along with its use.

With that in mind, there is one call site with num_to_pop == 1
in which you don't free any entry, and the other with num_to_pop == num_se
which seems to free all the members of the list, but the last one,
which is then freed by the caller.

This tells me you crammed two functions into one and you better
have one that pops a single element and another to destroy the list.

Benny

>> +
>> +	if (unlikely(num_to_pop <= 0))
>> +		return rv;
> 
> How unlikely is it?
> Is doing the extra compare really worth saving the spin_lock?
> 
>> +
>> +	spin_lock(&marks->im_lock);
>> +	while (!list_empty(&marks->im_extents) && num_to_pop-- > 0) {
>> +		rv = list_entry((&marks->im_extents)->next,
>> +				struct pnfs_block_short_extent, bse_node);
>> +		list_del_init(&rv->bse_node);
>> +		if (num_to_pop)
>> +			kfree(rv);
> 
> Please correct me if I'm wrong, you don't want to free the last element
> you pop since you want to return it. This is worth a comment...
> 
> I'd consider moving the decrement expression down here or
> changing the loop to be a for loop to improve its readability.
> In the latter case this will say if (num_to_pop > 1) kfree(rv)
> which is more straight forward IMHO.
> 
> Benny
> 
>> +	}
>> +	spin_unlock(&marks->im_lock);
>> +
>> +	BUG_ON(num_to_pop > 0);
>> +
>> +	return rv;
>> +}