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Diffstat (limited to 'doc/developer-guide/datastructure-mem-pool.md')
| -rw-r--r-- | doc/developer-guide/datastructure-mem-pool.md | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/doc/developer-guide/datastructure-mem-pool.md b/doc/developer-guide/datastructure-mem-pool.md index c71aa2a8ddd..225567cbf9f 100644 --- a/doc/developer-guide/datastructure-mem-pool.md +++ b/doc/developer-guide/datastructure-mem-pool.md @@ -1,5 +1,5 @@ -#Mem-pool -##Background +# Mem-pool +## Background There was a time when every fop in glusterfs used to incur cost of allocations/de-allocations for every stack wind/unwind between xlators because stack/frame/*_localt_t in every wind/unwind was allocated and de-allocated. Because of all these system calls in the fop path there was lot of latency and the worst part is that most of the times the number of frames/stacks active at any time wouldn't cross a threshold. So it was decided that this threshold number of frames/stacks would be allocated in the beginning of the process only once. Get one of them from the pool of stacks/frames whenever `STACK_WIND` is performed and put it back into the pool in `STACK_UNWIND`/`STACK_DESTROY` without incurring any extra system calls. The data structures are allocated only when threshold number of such items are in active use i.e. pool is in complete use.% increase in the performance once this was added to all the common data structures (inode/fd/dict etc) in xlators throughout the stack was tremendous. ## Data structure @@ -27,7 +27,7 @@ will be served from here until all the elements in the pool are in use i.e. cold }; ``` -##Life-cycle +## Life-cycle ``` mem_pool_new (data_type, unsigned long count) @@ -120,5 +120,5 @@ mem_pool_destroy (struct mem_pool *pool) Deletes this pool from the `global_list` maintained by `glusterfs-ctx` and frees all the memory allocated in `mem_pool_new`. -###How to pick pool-size +### How to pick pool-size This varies from work-load to work-load. Create the mem-pool with some random size and run the work-load. Take the statedump after the work-load is complete. In the statedump if `max_alloc` is always less than `cold_count` may be reduce the size of the pool closer to `max_alloc`. On the otherhand if there are lots of `pool-misses` then increase the `pool_size` by `max_stdalloc` to achieve better 'hit-rate' of the pool. |