details: http://hg.nginx.org/nginx/rev/d0404c9a7675
branches:
changeset: 6826:d0404c9a7675
user: Ruslan Ermilov <ru@nginx.com>
date: Wed Dec 07 22:25:37 2016 +0300
description:
Slab: simplified allocation from slots.

Removed code that would cause an endless loop, and removed condition
check that is always false. The first page in the slot list is
guaranteed to satisfy an allocation.

diffstat:

src/core/ngx_slab.c | 150 ++++++++++++++++++++++-----------------------------
1 files changed, 66 insertions(+), 84 deletions(-)

diffs (193 lines):

diff -r f6beb55792de -r d0404c9a7675 src/core/ngx_slab.c
--- a/src/core/ngx_slab.c Wed Dec 07 22:25:37 2016 +0300
+++ b/src/core/ngx_slab.c Wed Dec 07 22:25:37 2016 +0300
@@ -215,84 +215,71 @@ ngx_slab_alloc_locked(ngx_slab_pool_t *p

if (shift < ngx_slab_exact_shift) {

- do {
- bitmap = (uintptr_t *) ngx_slab_page_addr(pool, page);
-
- map = (1 << (ngx_pagesize_shift - shift))
- / (sizeof(uintptr_t) * 8);
-
- for (n = 0; n < map; n++) {
-
- if (bitmap[n] != NGX_SLAB_BUSY) {
-
- for (m = 1, i = 0; m; m <<= 1, i++) {
- if (bitmap[n] & m) {
- continue;
- }
-
- bitmap[n] |= m;
-
- i = ((n * sizeof(uintptr_t) * 8) << shift)
- + (i << shift);
-
- if (bitmap[n] == NGX_SLAB_BUSY) {
- for (n = n + 1; n < map; n++) {
- if (bitmap[n] != NGX_SLAB_BUSY) {
- p = (uintptr_t) bitmap + i;
+ bitmap = (uintptr_t *) ngx_slab_page_addr(pool, page);

- goto done;
- }
- }
-
- prev = ngx_slab_page_prev(page);
- prev->next = page->next;
- page->next->prev = page->prev;
-
- page->next = NULL;
- page->prev = NGX_SLAB_SMALL;
- }
+ map = (1 << (ngx_pagesize_shift - shift))
+ / (sizeof(uintptr_t) * 8);

- p = (uintptr_t) bitmap + i;
-
- goto done;
- }
- }
- }
+ for (n = 0; n < map; n++) {

- page = page->next;
-
- } while (page);
-
- } else if (shift == ngx_slab_exact_shift) {
-
- do {
- if (page->slab != NGX_SLAB_BUSY) {
+ if (bitmap[n] != NGX_SLAB_BUSY) {

for (m = 1, i = 0; m; m <<= 1, i++) {
- if (page->slab & m) {
+ if (bitmap[n] & m) {
continue;
}

- page->slab |= m;
+ bitmap[n] |= m;

- if (page->slab == NGX_SLAB_BUSY) {
+ i = ((n * sizeof(uintptr_t) * 8) << shift)
+ + (i << shift);
+
+ if (bitmap[n] == NGX_SLAB_BUSY) {
+ for (n = n + 1; n < map; n++) {
+ if (bitmap[n] != NGX_SLAB_BUSY) {
+ p = (uintptr_t) bitmap + i;
+
+ goto done;
+ }
+ }
+
prev = ngx_slab_page_prev(page);
prev->next = page->next;
page->next->prev = page->prev;

page->next = NULL;
- page->prev = NGX_SLAB_EXACT;
+ page->prev = NGX_SLAB_SMALL;
}

- p = ngx_slab_page_addr(pool, page) + (i << shift);
+ p = (uintptr_t) bitmap + i;

goto done;
}
}
+ }

- page = page->next;
+ } else if (shift == ngx_slab_exact_shift) {

- } while (page);
+ for (m = 1, i = 0; m; m <<= 1, i++) {
+ if (page->slab & m) {
+ continue;
+ }
+
+ page->slab |= m;
+
+ if (page->slab == NGX_SLAB_BUSY) {
+ prev = ngx_slab_page_prev(page);
+ prev->next = page->next;
+ page->next->prev = page->prev;
+
+ page->next = NULL;
+ page->prev = NGX_SLAB_EXACT;
+ }
+
+ p = ngx_slab_page_addr(pool, page) + (i << shift);
+
+ goto done;
+ }

} else { /* shift > ngx_slab_exact_shift */

@@ -301,38 +288,33 @@ ngx_slab_alloc_locked(ngx_slab_pool_t *p
n = ((uintptr_t) 1 << n) - 1;
mask = n << NGX_SLAB_MAP_SHIFT;

- do {
- if ((page->slab & NGX_SLAB_MAP_MASK) != mask) {
-
- for (m = (uintptr_t) 1 << NGX_SLAB_MAP_SHIFT, i = 0;
- m & mask;
- m <<= 1, i++)
- {
- if (page->slab & m) {
- continue;
- }
-
- page->slab |= m;
-
- if ((page->slab & NGX_SLAB_MAP_MASK) == mask) {
- prev = ngx_slab_page_prev(page);
- prev->next = page->next;
- page->next->prev = page->prev;
-
- page->next = NULL;
- page->prev = NGX_SLAB_BIG;
- }
-
- p = ngx_slab_page_addr(pool, page) + (i << shift);
-
- goto done;
- }
+ for (m = (uintptr_t) 1 << NGX_SLAB_MAP_SHIFT, i = 0;
+ m & mask;
+ m <<= 1, i++)
+ {
+ if (page->slab & m) {
+ continue;
}

- page = page->next;
+ page->slab |= m;

- } while (page);
+ if ((page->slab & NGX_SLAB_MAP_MASK) == mask) {
+ prev = ngx_slab_page_prev(page);
+ prev->next = page->next;
+ page->next->prev = page->prev;
+
+ page->next = NULL;
+ page->prev = NGX_SLAB_BIG;
+ }
+
+ p = ngx_slab_page_addr(pool, page) + (i << shift);
+
+ goto done;
+ }
}
+
+ ngx_slab_error(pool, NGX_LOG_ALERT, "ngx_slab_alloc(): page is busy");
+ ngx_debug_point();
}

page = ngx_slab_alloc_pages(pool, 1);
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