[PATCH] Core: bugfix for the ngx_slab_max_size case

[Maxim Dounin]

Hello!

On Wed, Jun 18, 2014 at 05:00:14PM +0800, Jianjun Zheng wrote:

> At present, alloting memory with size of ngx_slab_max_size causes
> 
> 1) an internal fragmentation, size of ngx_slab_max_size, comes into being
> 
> 2) the slot with index of (ngx_pagesize_shift - pool->min_shift - 1)
>     is the right slot for this size.
> 
> 
> # HG changeset patch
> # User Jianjun Zheng <codeeply at gmail.com>
> # Date 1403080799 -28800
> #      Wed Jun 18 16:39:59 2014 +0800
> # Node ID 1704335dd810e2e2abb2b393b4f7b7c9004c6012
> # Parent  ec919574cc14f7781c0ca212cffec586f88eec40
> Core: bugfix for the ngx_slab_max_size case
> 
> diff -r ec919574cc14 -r 1704335dd810 src/core/ngx_slab.c
> --- a/src/core/ngx_slab.c Tue Jun 17 16:51:25 2014 +0400
> +++ b/src/core/ngx_slab.c Wed Jun 18 16:39:59 2014 +0800
> @@ -160,7 +160,7 @@
>      ngx_uint_t        i, slot, shift, map;
>      ngx_slab_page_t  *page, *prev, *slots;
> 
> -    if (size >= ngx_slab_max_size) {
> +    if (size > ngx_slab_max_size) {
> 
>          ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, ngx_cycle->log, 0,
>                         "slab alloc: %uz", size);

Sorry for late reply.

Yes, the patch is right, allocation of ngx_slab_max_size exactly 
(aka half page, 2048 bytes on platforms with 4k pages) can be 
satisfied from the largest slot and don't need the whole page to 
be allocated.  While it's a corner case, it's certainly can be 
important in some cases and worth fixing.

Committed, thanks.

-- 
Maxim Dounin
http://nginx.org/