Messages in this thread | | | Subject | Re: [PATCH 2/2] kfree_rcu() should use kfree_bulk() interface | From | Rao Shoaib <> | Date | Wed, 4 Apr 2018 00:16:06 -0700 |
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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
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