Messages in this thread | | | Subject | Re: [PATCH 2/2] kfree_rcu() should use kfree_bulk() interface | From | Rao Shoaib <> | Date | Wed, 4 Apr 2018 01:39:07 -0700 |
| |
On 04/04/2018 12:16 AM, Rao Shoaib wrote: > > > On 04/03/2018 07:23 PM, Matthew Wilcox wrote: >> On Tue, Apr 03, 2018 at 05:55:55PM -0700, Rao Shoaib wrote: >>> On 04/03/2018 01:58 PM, Matthew Wilcox wrote: >>>> I think you might be better off with an IDR. The IDR can always >>>> contain one entry, so there's no need for this 'rbf_list_head' or >>>> __rcu_bulk_schedule_list. The IDR contains its first 64 entries in >>>> an array (if that array can be allocated), so it's compatible with the >>>> kfree_bulk() interface. >>>> >>> I have just familiarized myself with what IDR is by reading your >>> article. If >>> I am incorrect please correct me. >>> >>> The list and head you have pointed are only used if the container >>> can not >>> be allocated. That could happen with IDR as well. Note that the >>> containers >>> are allocated at boot time and are re-used. >> No, it can't happen with the IDR. The IDR can always contain one entry >> without allocating anything. If you fail to allocate the second entry, >> just free the first entry. >> >>> IDR seems to have some overhead, such as I have to specifically add the >>> pointer and free the ID, plus radix tree maintenance. >> ... what? Adding a pointer is simply idr_alloc(), and you get back an >> integer telling you which index it has. Your data structure has its >> own set of overhead. > The only overhead is a pointer that points to the head and an int to > keep count. If I use idr, I would have to allocate an struct idr which > is much larger. idr_alloc()/idr_destroy() operations are much more > costly than updating two pointers. As the pointers are stored in > slots/nodes corresponding to the id, I would have to retrieve the > pointers by calling idr_remove() to pass them to be freed, the > slots/nodes would constantly be allocated and freed. > > IDR is a very useful interface for allocating/managing ID's but I > really do not see the justification for using it over here, perhaps > you can elaborate more on the benefits and also on how I can just pass > the array to be freed. > > Shoaib > I may have mis-understood your comment. You are probably suggesting that I use IDR instead of allocating following containers.
+ struct rcu_bulk_free_container *rbf_container; + struct rcu_bulk_free_container *rbf_cached_container;
IDR uses radix_tree_node which allocates following two arrays. since I do not need any ID's why not just use the radix_tree_node directly, but I do not need a radix tree either, so why not just use an array. That is what I am doing.
void __rcu *slots[RADIX_TREE_MAP_SIZE]; unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS]; ==> Not needed
As far as allocation failure is concerned, the allocation has to be done at run time. If the allocation of a container can fail, so can the allocation of radix_tree_node as it also requires memory.
I really do not see any advantages of using IDR. The structure I have is much simpler and does exactly what I need.
Shoaib
| |