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Core: slab allocator free pages defragmentation.

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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.
This commit is contained in:
Maxim Dounin 2014-06-03 17:53:03 +04:00
parent 9b5a17b5e2
commit afb4aafc6e
2 changed files with 60 additions and 1 deletions
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60
src/core/ngx_slab.c
View File

@ -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 *pool, ngx_uint_t pages)
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 *pool, ngx_slab_page_t *page,
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;

1
src/core/ngx_slab.h
View File

@ -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;