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DOC: pool: document the purpose of various structures in the code

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The pools have become complex with the shared pools and the thread-local
caches, and the purpose of certain structures is never easy to grasp.
Let's add a bit of documentation there to save some long and painful
analysis to those touching that area.
This commit is contained in:
Willy Tarreau 2021-12-30 16:35:32 +01:00
parent d5ec100661
commit 4859984a5b
1 changed files with 14 additions and 0 deletions
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14
include/haproxy/pool-t.h
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@ -56,16 +56,30 @@
#define POOL_F_NO_FAIL 0x00000004 // do not randomly fail
/* This is the head of a thread-local cache */
struct pool_cache_head {
struct list list; /* head of objects in this pool */
unsigned int count; /* number of objects in this pool */
} THREAD_ALIGNED(64);
/* This represents one item stored in the thread-local cache. <by_pool> links
* the object to the list of objects in the pool, and <by_lru> links the object
* to the local thread's list of hottest objects. This way it's possible to
* allocate a fresh object from the cache, or to release cold objects from any
* pool (no bookkeeping is needed since shared pools do not know how many
* objects they store).
*/
struct pool_cache_item {
struct list by_pool; /* link to objects in this pool */
struct list by_lru; /* link to objects by LRU order */
};
/* This describes a complete pool, with its status, usage statistics and the
* thread-local caches if any. Even if pools are disabled, these descriptors
* are valid and are used at least to get names and sizes. For small builds
* using neither threads nor pools, this structure might be reduced, and
* alignment could be removed.
*/
struct pool_head {
void **free_list;
unsigned int used; /* how many chunks are currently in use */