[src/trunk]: src/sys/kern Move some code into a separate function, and explai...

[maxv <maxv%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/360a70f18262
branches:  trunk
changeset: 449713:360a70f18262
user:      maxv <maxv%NetBSD.org@localhost>
date:      Sun Mar 17 14:52:25 2019 +0000

description:
Move some code into a separate function, and explain a bit. Also define
PHSIZE. No functional change.

diffstat:

 sys/kern/subr_pool.c |  62 ++++++++++++++++++++++++++++++++++++---------------
 1 files changed, 43 insertions(+), 19 deletions(-)

diffs (108 lines):

diff -r 77fe8b970912 -r 360a70f18262 sys/kern/subr_pool.c
--- a/sys/kern/subr_pool.c      Sun Mar 17 14:11:48 2019 +0000
+++ b/sys/kern/subr_pool.c      Sun Mar 17 14:52:25 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_pool.c,v 1.239 2019/03/17 07:22:18 maxv Exp $     */
+/*     $NetBSD: subr_pool.c,v 1.240 2019/03/17 14:52:25 maxv Exp $     */
 
 /*
  * Copyright (c) 1997, 1999, 2000, 2002, 2007, 2008, 2010, 2014, 2015, 2018
@@ -33,7 +33,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_pool.c,v 1.239 2019/03/17 07:22:18 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_pool.c,v 1.240 2019/03/17 14:52:25 maxv Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ddb.h"
@@ -177,6 +177,8 @@
 #define        ph_itemlist     ph_u.phu_normal.phu_itemlist
 #define        ph_bitmap       ph_u.phu_notouch.phu_bitmap
 
+#define PHSIZE ALIGN(sizeof(struct pool_item_header))
+
 #if defined(DIAGNOSTIC) && !defined(KASAN)
 #define POOL_CHECK_MAGIC
 #endif
@@ -566,6 +568,37 @@
            0, 0, "pcachecpu", &pool_allocator_meta, IPL_NONE);
 }
 
+static inline bool
+pool_init_is_phinpage(const struct pool *pp)
+{
+       size_t pagesize;
+
+       if (pp->pr_roflags & PR_PHINPAGE) {
+               return true;
+       }
+       if (pp->pr_roflags & (PR_NOTOUCH | PR_NOALIGN)) {
+               return false;
+       }
+
+       pagesize = pp->pr_alloc->pa_pagesz;
+
+       /*
+        * Threshold: the item size is below 1/16 of a page size, and below
+        * 8 times the page header size. The latter ensures we go off-page
+        * if the page header would make us waste a rather big item.
+        */
+       if (pp->pr_size < MIN(pagesize / 16, PHSIZE * 8)) {
+               return true;
+       }
+
+       /* Put the header into the page if it doesn't waste any items. */
+       if (pagesize / pp->pr_size == (pagesize - PHSIZE) / pp->pr_size) {
+               return true;
+       }
+
+       return false;
+}
+
 /*
  * Initialize the given pool resource structure.
  *
@@ -577,7 +610,7 @@
     const char *wchan, struct pool_allocator *palloc, int ipl)
 {
        struct pool *pp1;
-       size_t trysize, phsize, prsize;
+       size_t prsize;
        int itemspace, slack;
 
        /* XXX ioff will be removed. */
@@ -667,26 +700,17 @@
        pp->pr_drain_hook_arg = NULL;
        pp->pr_freecheck = NULL;
        pool_redzone_init(pp, size);
+       pp->pr_itemoffset = 0;
 
        /*
-        * Decide whether to put the page header off page to avoid wasting too
-        * large a part of the page or too big item. Off-page page headers go
-        * on a hash table, so we can match a returned item with its header
-        * based on the page address. We use 1/16 of the page size and about 8
-        * times of the item size as the threshold. (XXX: tune)
-        *
-        * However, we'll put the header into the page if we can put it without
-        * wasting any items.
+        * Decide whether to put the page header off-page to avoid wasting too
+        * large a part of the page or too big an item. Off-page page headers
+        * go on a hash table, so we can match a returned item with its header
+        * based on the page address.
         */
-       pp->pr_itemoffset = 0;
-       trysize = palloc->pa_pagesz;
-       phsize = ALIGN(sizeof(struct pool_item_header));
-       if (pp->pr_roflags & PR_PHINPAGE ||
-           ((pp->pr_roflags & (PR_NOTOUCH | PR_NOALIGN)) == 0 &&
-           (pp->pr_size < MIN(palloc->pa_pagesz / 16, phsize << 3) ||
-           trysize / pp->pr_size == (trysize - phsize) / pp->pr_size))) {
+       if (pool_init_is_phinpage(pp)) {
                /* Use the end of the page for the page header */
-               itemspace = palloc->pa_pagesz - phsize;
+               itemspace = palloc->pa_pagesz - PHSIZE;
                pp->pr_phoffset = itemspace;
                pp->pr_roflags |= PR_PHINPAGE;
        } else {