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[RFC] Concept: Active/busy "reverse" mapping
The goal of this code is to make sure that used pages are marked as such.
This is accomplished by:
* When a process is descheduled - look in its mm for used pages - update
corresponding page. (Done at most once per tick)
Pros:
* No need for extra elements in page
* Used page will be updated promptly
Cons:
* Context switch times will increase
* CPU cycle waste.
But:
* On my UP it does not affect performance that much :-)
- Lost at most 1,7 MB/s (-7%)
+ Gained in some cases (read, diff, dbench 4%)
[I thought it would become much worse - with other mm changes
compensating]
--
Roger Larsson
Skellefteċ
Sweden
*******************************************
Patch prepared by: roger.larsson@norran.net
Name of file: /home/roger/patches/patch-2.4.17rc1-update_page_usage_R2
--- linux/kernel/sched.c.orig Thu Dec 13 23:33:30 2001
+++ linux/kernel/sched.c Wed Dec 19 23:27:46 2001
@@ -557,6 +557,10 @@
spin_lock_prefetch(&runqueue_lock);
if (!current->active_mm) BUG();
+
+ if (current->mm)
+ update_page_usage(current->mm);
+
need_resched_back:
prev = current;
this_cpu = prev->processor;
--- linux/mm/vmscan.c.orig Thu Dec 13 23:30:55 2001
+++ linux/mm/vmscan.c Wed Dec 19 23:27:46 2001
@@ -246,28 +246,16 @@
return count;
}
-/* Placeholder for swap_out(): may be updated by fork.c:mmput() */
-struct mm_struct *swap_mm = &init_mm;
-
/*
- * Returns remaining count of pages to be swapped out by followup call.
+ * No checking of mm nor address, and no locking...
*/
-static inline int swap_out_mm(struct mm_struct * mm, int count, int * mmcounter, zone_t * classzone)
+static inline int _swap_out_mm(struct mm_struct * mm, unsigned long address, int count, zone_t * classzone)
{
- unsigned long address;
struct vm_area_struct* vma;
-
/*
* Find the proper vm-area after freezing the vma chain
* and ptes.
*/
- spin_lock(&mm->page_table_lock);
- address = mm->swap_address;
- if (address == TASK_SIZE || swap_mm != mm) {
- /* We raced: don't count this mm but try again */
- ++*mmcounter;
- goto out_unlock;
- }
vma = find_vma(mm, address);
if (vma) {
if (address < vma->vm_start)
@@ -279,14 +267,36 @@
if (!vma)
break;
if (!count)
- goto out_unlock;
+ return count;
address = vma->vm_start;
}
}
/* Indicate that we reached the end of address space */
mm->swap_address = TASK_SIZE;
+ mm->update_jiffies = jiffies;
+
+ return count;
+}
+
+/* Placeholder for swap_out(): may be updated by fork.c:mmput() */
+struct mm_struct *swap_mm = &init_mm;
+
+/*
+ * Returns remaining count of pages to be swapped out by followup call.
+ */
+static inline int swap_out_mm(struct mm_struct * mm, int count, int * mmcounter, zone_t * classzone)
+{
+ unsigned long address;
+
+ spin_lock(&mm->page_table_lock);
+ address = mm->swap_address;
+ if (address == TASK_SIZE || swap_mm != mm) {
+ /* We raced: don't count this mm but try again */
+ ++*mmcounter;
+ }
+ else
+ count = _swap_out_mm(mm, address, count, classzone);
-out_unlock:
spin_unlock(&mm->page_table_lock);
return count;
}
@@ -333,6 +343,29 @@
return 0;
}
+
+void update_page_usage(struct mm_struct *mm)
+{
+ unsigned long address;
+
+ atomic_inc(&mm->mm_users); /* needed? */
+
+ /* statistics...
+ * - no more then once a jiffie
+ * - no need to do an expensive spin...
+ */
+ if (mm->update_jiffies != jiffies &&
+ spin_trylock(&mm->page_table_lock)) {
+ address = mm->swap_address;
+ if (address == TASK_SIZE)
+ address = 0;
+ (void)_swap_out_mm(mm, address, 1, NULL);
+
+ spin_unlock(&mm->page_table_lock);
+ }
+
+ mmput(mm); /* atomic_dec */
+}
static int FASTCALL(shrink_cache(int nr_pages, zone_t * classzone, unsigned int gfp_mask, int priority));
static int shrink_cache(int nr_pages, zone_t * classzone, unsigned int gfp_mask, int priority)
--- linux/include/linux/mm.h.orig Fri Dec 7 18:47:03 2001
+++ linux/include/linux/mm.h Wed Dec 19 23:31:05 2001
@@ -423,6 +423,9 @@
extern void ptrace_disable(struct task_struct *);
extern int ptrace_check_attach(struct task_struct *task, int kill);
+int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start,
+ int len, int write, int force, struct page **pages, struct vm_area_struct **vmas);
+
/*
* On a two-level page table, this ends up being trivial. Thus the
* inlining and the symmetry break with pte_alloc() that does all
@@ -558,11 +561,13 @@
* before relocating the vma range ourself.
*/
address &= PAGE_MASK;
+ spin_lock(&vma->vm_mm->page_table_lock);
grow = (vma->vm_start - address) >> PAGE_SHIFT;
if (vma->vm_end - address > current->rlim[RLIMIT_STACK].rlim_cur ||
- ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) > current->rlim[RLIMIT_AS].rlim_cur)
+ ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) > current->rlim[RLIMIT_AS].rlim_cur) {
+ spin_unlock(&vma->vm_mm->page_table_lock);
return -ENOMEM;
- spin_lock(&vma->vm_mm->page_table_lock);
+ }
vma->vm_start = address;
vma->vm_pgoff -= grow;
vma->vm_mm->total_vm += grow;
--- linux/include/linux/mmzone.h.orig Thu Dec 13 23:42:46 2001
+++ linux/include/linux/mmzone.h Wed Dec 19 23:27:46 2001
@@ -113,8 +113,9 @@
extern int numnodes;
extern pg_data_t *pgdat_list;
-#define memclass(pgzone, classzone) (((pgzone)->zone_pgdat == (classzone)->zone_pgdat) \
- && ((pgzone) <= (classzone)))
+/* with this change classzone might be zero! */
+#define memclass(pgzone, classzone) (((pgzone) <= (classzone)) && \
+ ((pgzone)->zone_pgdat == (classzone)->zone_pgdat))
/*
* The following two are not meant for general usage. They are here as
--- linux/Makefile.orig Thu Dec 13 23:33:22 2001
+++ linux/Makefile Wed Dec 19 23:28:28 2001
@@ -1,7 +1,7 @@
VERSION = 2
PATCHLEVEL = 4
SUBLEVEL = 17
-EXTRAVERSION = -rc1
+EXTRAVERSION = -rc1-update_page_usage
KERNELRELEASE=$(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)