[src/trunk]: src/sys/uvm struct vm_page: cluster fields most heavily used by ...

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

details:   https://anonhg.NetBSD.org/src/rev/4a71e00a7492
branches:  trunk
changeset: 968013:4a71e00a7492
user:      ad <ad%NetBSD.org@localhost>
date:      Tue Dec 31 17:56:16 2019 +0000

description:
struct vm_page: cluster fields most heavily used by the page allocator and
uvmpdpol at the start of the structure, so that while under global lock we
need only touch one cache line for each vm_page.  There is still the problem
of vm_page not being aligned, but this seems to drop lock wait time for
(a modified) uvmpdpol and the allocator by 20-30% in a quick test.

diffstat:

 sys/uvm/uvm_page.h |  23 +++++++++++++++--------
 1 files changed, 15 insertions(+), 8 deletions(-)

diffs (47 lines):

diff -r acaa0be2255f -r 4a71e00a7492 sys/uvm/uvm_page.h
--- a/sys/uvm/uvm_page.h        Tue Dec 31 17:26:04 2019 +0000
+++ b/sys/uvm/uvm_page.h        Tue Dec 31 17:56:16 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_page.h,v 1.91 2019/12/31 12:40:27 ad Exp $ */
+/*     $NetBSD: uvm_page.h,v 1.92 2019/12/31 17:56:16 ad Exp $ */
 
 /*
  * Copyright (c) 1997 Charles D. Cranor and Washington University.
@@ -142,6 +142,13 @@
  * - uvm_pagefree: owned by a uvm_object/vm_anon -> free
  * - uvm_pglistalloc: free -> allocated by uvm_pglistalloc
  * - uvm_pglistfree: allocated by uvm_pglistalloc -> free
+ *
+ * On the ordering of fields:
+ *
+ * The fields most heavily used by the page allocator and uvmpdpol are
+ * clustered together at the start of the structure, so that while under
+ * global lock it's more likely that only one cache line for each page need
+ * be touched.
  */
 
 struct vm_page {
@@ -151,16 +158,16 @@
                LIST_ENTRY(vm_page) list;       /* f: global free page queue */
        } pageq;
        TAILQ_ENTRY(vm_page)    pdqueue;        /* p: pagedaemon queue */
+       kmutex_t                interlock;      /* s: lock on identity */
+       uint32_t                pqflags;        /* i: pagedaemon flags */
+       uint16_t                flags;          /* o: object flags */
+       uint16_t                spare;          /*  : spare for now */
+       paddr_t                 phys_addr;      /* o: physical address of pg */
+       uint32_t                loan_count;     /* o,i: num. active loans */
+       uint32_t                wire_count;     /* o,i: wired down map refs */
        struct vm_anon          *uanon;         /* o,i: anon */
        struct uvm_object       *uobject;       /* o,i: object */
        voff_t                  offset;         /* o: offset into object */
-       uint16_t                flags;          /* o: object flags */
-       uint16_t                spare;          /*  : spare for now */
-       uint32_t                pqflags;        /* p: pagedaemon flags */
-       uint32_t                loan_count;     /* o,i: num. active loans */
-       uint32_t                wire_count;     /* o,i: wired down map refs */
-       paddr_t                 phys_addr;      /* o: physical address of pg */
-       kmutex_t                interlock;      /* s: lock on identity */
 
 #ifdef __HAVE_VM_PAGE_MD
        struct vm_page_md       mdpage;         /* ?: pmap-specific data */