details: http://hg.nginx.org/nginx/rev/c46657e391a3
branches:
changeset: 5718:c46657e391a3
user: Maxim Dounin <mdounin@mdounin.ru>
date: Tue Jun 03 17:53:03 2014 +0400
description:
Core: slab allocator free pages defragmentation.

Large allocations from a slab pool result in free page blocks being fragmented,
eventually leading to a situation when no further allocation larger than a page
size are possible from the pool. While this isn't a problem for nginx itself,
it is known to be bad for various 3rd party modules. Fix is to merge adjacent
blocks of free pages in the ngx_slab_free_pages() function.

Prodded by Wandenberg Peixoto and Yichun Zhang.

diffstat:

src/core/ngx_slab.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
src/core/ngx_slab.h | 1 +
2 files changed, 60 insertions(+), 1 deletions(-)

diffs (102 lines):

diff --git a/src/core/ngx_slab.c b/src/core/ngx_slab.c
--- a/src/core/ngx_slab.c
+++ b/src/core/ngx_slab.c
@@ -129,6 +129,8 @@ ngx_slab_init(ngx_slab_pool_t *pool)
pool->pages->slab = pages;
}

+ pool->last = pool->pages + pages;
+
pool->log_nomem = 1;
pool->log_ctx = &pool->zero;
pool->zero = '\0';
@@ -626,6 +628,8 @@ ngx_slab_alloc_pages(ngx_slab_pool_t *po
if (page->slab >= pages) {

if (page->slab > pages) {
+ page[page->slab - 1].prev = (uintptr_t) &page[pages];
+
page[pages].slab = page->slab - pages;
page[pages].next = page->next;
page[pages].prev = page->prev;
@@ -672,7 +676,8 @@ static void
ngx_slab_free_pages(ngx_slab_pool_t *pool, ngx_slab_page_t *page,
ngx_uint_t pages)
{
- ngx_slab_page_t *prev;
+ ngx_uint_t type;
+ ngx_slab_page_t *prev, *join;

page->slab = pages--;

@@ -686,6 +691,59 @@ ngx_slab_free_pages(ngx_slab_pool_t *poo
page->next->prev = page->prev;
}

+ join = page + page->slab;
+
+ if (join < pool->last) {
+ type = join->prev & NGX_SLAB_PAGE_MASK;
+
+ if (type == NGX_SLAB_PAGE) {
+
+ if (join->next != NULL) {
+ pages += join->slab;
+ page->slab += join->slab;
+
+ prev = (ngx_slab_page_t *) (join->prev & ~NGX_SLAB_PAGE_MASK);
+ prev->next = join->next;
+ join->next->prev = join->prev;
+
+ join->slab = NGX_SLAB_PAGE_FREE;
+ join->next = NULL;
+ join->prev = NGX_SLAB_PAGE;
+ }
+ }
+ }
+
+ if (page > pool->pages) {
+ join = page - 1;
+ type = join->prev & NGX_SLAB_PAGE_MASK;
+
+ if (type == NGX_SLAB_PAGE) {
+
+ if (join->slab == NGX_SLAB_PAGE_FREE) {
+ join = (ngx_slab_page_t *) (join->prev & ~NGX_SLAB_PAGE_MASK);
+ }
+
+ if (join->next != NULL) {
+ pages += join->slab;
+ join->slab += page->slab;
+
+ prev = (ngx_slab_page_t *) (join->prev & ~NGX_SLAB_PAGE_MASK);
+ prev->next = join->next;
+ join->next->prev = join->prev;
+
+ page->slab = NGX_SLAB_PAGE_FREE;
+ page->next = NULL;
+ page->prev = NGX_SLAB_PAGE;
+
+ page = join;
+ }
+ }
+ }
+
+ if (pages) {
+ page[pages].prev = (uintptr_t) page;
+ }
+
page->prev = (uintptr_t) &pool->free;
page->next = pool->free.next;

diff --git a/src/core/ngx_slab.h b/src/core/ngx_slab.h
--- a/src/core/ngx_slab.h
+++ b/src/core/ngx_slab.h
@@ -29,6 +29,7 @@ typedef struct {
size_t min_shift;

ngx_slab_page_t *pages;
+ ngx_slab_page_t *last;
ngx_slab_page_t free;

u_char *start;

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