details: http://hg.nginx.org/nginx/rev/c9d680b00744
branches:
changeset: 6445:c9d680b00744
user: Dmitry Volyntsev <xeioex@nginx.com>
date: Fri Mar 18 15:08:21 2016 +0300
description:
Cache: added watermark to reduce IO load when keys_zone is full.

When a keys_zone is full then each next request to the cache is
penalized. That is, the cache has to evict older files to get a
slot from the keys_zone synchronously. The patch introduces new
behavior in this scenario. Manager will try to maintain available
free slots in the keys_zone by cleaning old files in the background.

diffstat:

src/http/ngx_http_cache.h | 2 ++
src/http/ngx_http_file_cache.c | 39 +++++++++++++++++++++++++++++++++------
2 files changed, 35 insertions(+), 6 deletions(-)

diffs (133 lines):

diff -r 043914d19be8 -r c9d680b00744 src/http/ngx_http_cache.h
--- a/src/http/ngx_http_cache.h Fri Mar 18 14:27:30 2016 +0300
+++ b/src/http/ngx_http_cache.h Fri Mar 18 15:08:21 2016 +0300
@@ -138,6 +138,8 @@ typedef struct {
ngx_atomic_t cold;
ngx_atomic_t loading;
off_t size;
+ ngx_uint_t count;
+ ngx_uint_t watermark;
} ngx_http_file_cache_sh_t;


diff -r 043914d19be8 -r c9d680b00744 src/http/ngx_http_file_cache.c
--- a/src/http/ngx_http_file_cache.c Fri Mar 18 14:27:30 2016 +0300
+++ b/src/http/ngx_http_file_cache.c Fri Mar 18 15:08:21 2016 +0300
@@ -62,6 +62,7 @@ static ngx_int_t ngx_http_file_cache_add
ngx_http_cache_t *c);
static ngx_int_t ngx_http_file_cache_delete_file(ngx_tree_ctx_t *ctx,
ngx_str_t *path);
+static void ngx_http_file_cache_set_watermark(ngx_http_file_cache_t *cache);


ngx_str_t ngx_http_cache_status[] = {
@@ -147,6 +148,8 @@ ngx_http_file_cache_init(ngx_shm_zone_t
cache->sh->cold = 1;
cache->sh->loading = 0;
cache->sh->size = 0;
+ cache->sh->count = 0;
+ cache->sh->watermark = (ngx_uint_t) -1;

cache->bsize = ngx_fs_bsize(cache->path->name.data);

@@ -861,6 +864,8 @@ ngx_http_file_cache_exists(ngx_http_file
fcn = ngx_slab_calloc_locked(cache->shpool,
sizeof(ngx_http_file_cache_node_t));
if (fcn == NULL) {
+ ngx_http_file_cache_set_watermark(cache);
+
ngx_shmtx_unlock(&cache->shpool->mutex);

(void) ngx_http_file_cache_forced_expire(cache);
@@ -877,6 +882,8 @@ ngx_http_file_cache_exists(ngx_http_file
}
}

+ cache->sh->count++;
+
ngx_memcpy((u_char *) &fcn->node.key, c->key, sizeof(ngx_rbtree_key_t));

ngx_memcpy(fcn->key, &c->key[sizeof(ngx_rbtree_key_t)],
@@ -1631,6 +1638,7 @@ ngx_http_file_cache_free(ngx_http_cache_
ngx_queue_remove(&fcn->queue);
ngx_rbtree_delete(&cache->sh->rbtree, &fcn->node);
ngx_slab_free_locked(cache->shpool, fcn);
+ cache->sh->count--;
c->node = NULL;
}

@@ -1883,6 +1891,7 @@ ngx_http_file_cache_delete(ngx_http_file
ngx_queue_remove(q);
ngx_rbtree_delete(&cache->sh->rbtree, &fcn->node);
ngx_slab_free_locked(cache->shpool, fcn);
+ cache->sh->count--;
}
}

@@ -1892,8 +1901,9 @@ ngx_http_file_cache_manager(void *data)
{
ngx_http_file_cache_t *cache = data;

- off_t size;
- time_t next, wait;
+ off_t size;
+ time_t next, wait;
+ ngx_uint_t count, watermark;

next = ngx_http_file_cache_expire(cache);

@@ -1904,13 +1914,16 @@ ngx_http_file_cache_manager(void *data)
ngx_shmtx_lock(&cache->shpool->mutex);

size = cache->sh->size;
+ count = cache->sh->count;
+ watermark = cache->sh->watermark;

ngx_shmtx_unlock(&cache->shpool->mutex);

- ngx_log_debug1(NGX_LOG_DEBUG_HTTP, ngx_cycle->log, 0,
- "http file cache size: %O", size);
-
- if (size < cache->max_size) {
+ ngx_log_debug3(NGX_LOG_DEBUG_HTTP, ngx_cycle->log, 0,
+ "http file cache size: %O c:%ui w:%i",
+ size, count, (ngx_int_t) watermark);
+
+ if (size < cache->max_size && count < watermark) {
return next;
}

@@ -2094,12 +2107,16 @@ ngx_http_file_cache_add(ngx_http_file_ca
fcn = ngx_slab_calloc_locked(cache->shpool,
sizeof(ngx_http_file_cache_node_t));
if (fcn == NULL) {
+ ngx_http_file_cache_set_watermark(cache);
+
if (cache->fail_time != ngx_time()) {
cache->fail_time = ngx_time();
ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, 0,
"could not allocate node%s", cache->shpool->log_ctx);
}

+ cache->sh->count++;
+
ngx_shmtx_unlock(&cache->shpool->mutex);
return NGX_ERROR;
}
@@ -2146,6 +2163,16 @@ ngx_http_file_cache_delete_file(ngx_tree
}


+static void
+ngx_http_file_cache_set_watermark(ngx_http_file_cache_t *cache)
+{
+ cache->sh->watermark = cache->sh->count - cache->sh->count / 8;
+
+ ngx_log_debug1(NGX_LOG_DEBUG_HTTP, ngx_cycle->log, 0,
+ "http file cache watermark: %ui", cache->sh->watermark);
+}
+
+
time_t
ngx_http_file_cache_valid(ngx_array_t *cache_valid, ngx_uint_t status)
{

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