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SubjectRe: xmm2 - monitor Linux MM active/inactive lists graphically

On 26 Oct 2001, Zlatko Calusic wrote:
>
> When I find some time, I'll dig around that code. It is very
> interesting part of the kernel, I'm sure, I just didn't have enough
> time so far, to spend hacking on that part.

Attached is a very untested patch (but hey, it compiles, so it must work,
right?) against 2.4.14-pre2, that makes the batching be a high/low
watermark thing instead. It actually simplified the code, but that is, of
course, assuming that it works at all ;)

(If I got the comparisons wrong, of if I update the counts wrong, your IO
queue will probably stop cold. So be careful. The code is obvious
enough, but typos and thinkos happen).

Linus
diff -u --recursive pre2/linux/drivers/block/ll_rw_blk.c linux/drivers/block/ll_rw_blk.c
--- pre2/linux/drivers/block/ll_rw_blk.c Fri Oct 26 09:48:25 2001
+++ linux/drivers/block/ll_rw_blk.c Fri Oct 26 09:53:54 2001
@@ -140,21 +140,23 @@
return &blk_dev[MAJOR(dev)].request_queue;
}

-static int __blk_cleanup_queue(struct list_head *head)
+static int __blk_cleanup_queue(struct request_list *list)
{
+ struct list_head *head = &list->free;
struct request *rq;
int i = 0;

- if (list_empty(head))
- return 0;
-
- do {
+ while (!list_empty(head)) {
rq = list_entry(head->next, struct request, queue);
list_del(&rq->queue);
kmem_cache_free(request_cachep, rq);
i++;
- } while (!list_empty(head));
+ };

+ if (i != list->count)
+ printk("request list leak!\n");
+
+ list->count = 0;
return i;
}

@@ -176,10 +178,8 @@
{
int count = queue_nr_requests;

- count -= __blk_cleanup_queue(&q->request_freelist[READ]);
- count -= __blk_cleanup_queue(&q->request_freelist[WRITE]);
- count -= __blk_cleanup_queue(&q->pending_freelist[READ]);
- count -= __blk_cleanup_queue(&q->pending_freelist[WRITE]);
+ count -= __blk_cleanup_queue(&q->rq[READ]);
+ count -= __blk_cleanup_queue(&q->rq[WRITE]);

if (count)
printk("blk_cleanup_queue: leaked requests (%d)\n", count);
@@ -331,11 +331,10 @@
struct request *rq;
int i;

- INIT_LIST_HEAD(&q->request_freelist[READ]);
- INIT_LIST_HEAD(&q->request_freelist[WRITE]);
- INIT_LIST_HEAD(&q->pending_freelist[READ]);
- INIT_LIST_HEAD(&q->pending_freelist[WRITE]);
- q->pending_free[READ] = q->pending_free[WRITE] = 0;
+ INIT_LIST_HEAD(&q->rq[READ].free);
+ INIT_LIST_HEAD(&q->rq[WRITE].free);
+ q->rq[READ].count = 0;
+ q->rq[WRITE].count = 0;

/*
* Divide requests in half between read and write
@@ -349,7 +348,8 @@
}
memset(rq, 0, sizeof(struct request));
rq->rq_status = RQ_INACTIVE;
- list_add(&rq->queue, &q->request_freelist[i & 1]);
+ list_add(&rq->queue, &q->rq[i&1].free);
+ q->rq[i&1].count++;
}

init_waitqueue_head(&q->wait_for_request);
@@ -423,10 +423,12 @@
static inline struct request *get_request(request_queue_t *q, int rw)
{
struct request *rq = NULL;
+ struct request_list *rl = q->rq + rw;

- if (!list_empty(&q->request_freelist[rw])) {
- rq = blkdev_free_rq(&q->request_freelist[rw]);
+ if (!list_empty(&rl->free)) {
+ rq = blkdev_free_rq(&rl->free);
list_del(&rq->queue);
+ rl->count--;
rq->rq_status = RQ_ACTIVE;
rq->special = NULL;
rq->q = q;
@@ -443,17 +445,13 @@
register struct request *rq;
DECLARE_WAITQUEUE(wait, current);

+ generic_unplug_device(q);
add_wait_queue_exclusive(&q->wait_for_request, &wait);
- for (;;) {
- __set_current_state(TASK_UNINTERRUPTIBLE);
- spin_lock_irq(&io_request_lock);
- rq = get_request(q, rw);
- spin_unlock_irq(&io_request_lock);
- if (rq)
- break;
- generic_unplug_device(q);
- schedule();
- }
+ do {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ if (q->rq[rw].count < batch_requests)
+ schedule();
+ } while ((rq = get_request(q,rw)) == NULL);
remove_wait_queue(&q->wait_for_request, &wait);
current->state = TASK_RUNNING;
return rq;
@@ -542,15 +540,6 @@
list_add(&req->queue, insert_here);
}

-inline void blk_refill_freelist(request_queue_t *q, int rw)
-{
- if (q->pending_free[rw]) {
- list_splice(&q->pending_freelist[rw], &q->request_freelist[rw]);
- INIT_LIST_HEAD(&q->pending_freelist[rw]);
- q->pending_free[rw] = 0;
- }
-}
-
/*
* Must be called with io_request_lock held and interrupts disabled
*/
@@ -564,28 +553,12 @@

/*
* Request may not have originated from ll_rw_blk. if not,
- * asumme it has free buffers and check waiters
+ * assume it has free buffers and check waiters
*/
if (q) {
- /*
- * If nobody is waiting for requests, don't bother
- * batching up.
- */
- if (!list_empty(&q->request_freelist[rw])) {
- list_add(&req->queue, &q->request_freelist[rw]);
- return;
- }
-
- /*
- * Add to pending free list and batch wakeups
- */
- list_add(&req->queue, &q->pending_freelist[rw]);
-
- if (++q->pending_free[rw] >= batch_requests) {
- int wake_up = q->pending_free[rw];
- blk_refill_freelist(q, rw);
- wake_up_nr(&q->wait_for_request, wake_up);
- }
+ list_add(&req->queue, &q->rq[rw].free);
+ if (++q->rq[rw].count >= batch_requests && waitqueue_active(&q->wait_for_request))
+ wake_up(&q->wait_for_request);
}
}

@@ -1144,7 +1117,7 @@
/*
* Batch frees according to queue length
*/
- batch_requests = queue_nr_requests/3;
+ batch_requests = queue_nr_requests/4;
printk("block: %d slots per queue, batch=%d\n", queue_nr_requests, batch_requests);

#ifdef CONFIG_AMIGA_Z2RAM
diff -u --recursive pre2/linux/include/linux/blkdev.h linux/include/linux/blkdev.h
--- pre2/linux/include/linux/blkdev.h Tue Oct 23 22:01:01 2001
+++ linux/include/linux/blkdev.h Fri Oct 26 09:36:41 2001
@@ -66,14 +66,17 @@
*/
#define QUEUE_NR_REQUESTS 8192

+struct request_list {
+ unsigned int count;
+ struct list_head free;
+};
+
struct request_queue
{
/*
* the queue request freelist, one for reads and one for writes
*/
- struct list_head request_freelist[2];
- struct list_head pending_freelist[2];
- int pending_free[2];
+ struct request_list rq[2];

/*
* Together with queue_head for cacheline sharing
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