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SubjectRe: [with-PATCH-really] highmem deadlock removal, balancing & cleanup
On Fri, May 25, 2001 at 08:29:38PM -0400, Ben LaHaise wrote:
> amount of bounce buffers to guarentee progress while submitting io. The
> -ac kernels have a patch from Ingo that provides private pools for bounce
> buffers and buffer_heads. I went a step further and have a memory
> reservation patch that provides for memory pools being reserved against a
> particular zone. This is needed to prevent the starvation that irq
> allocations can cause.
>
> Some of these cleanups are 2.5 fodder, but we really need something in 2.4
> right now, so...

Please merge this one in 2.4 for now (originally from Ingo, I only
improved it), this is a real definitive fix and there's no nicer way to
handle that unless you want to generalize an API for people to generate
private anti-deadlock ("make sure to always make a progress") memory
pools:

diff -urN 2.4.4/mm/highmem.c highmem-deadlock/mm/highmem.c
--- 2.4.4/mm/highmem.c Sat Apr 28 05:24:48 2001
+++ highmem-deadlock/mm/highmem.c Sat Apr 28 18:21:24 2001
@@ -159,6 +159,19 @@
spin_unlock(&kmap_lock);
}

+#define POOL_SIZE 32
+
+/*
+ * This lock gets no contention at all, normally.
+ */
+static spinlock_t emergency_lock = SPIN_LOCK_UNLOCKED;
+
+int nr_emergency_pages;
+static LIST_HEAD(emergency_pages);
+
+int nr_emergency_bhs;
+static LIST_HEAD(emergency_bhs);
+
/*
* Simple bounce buffer support for highmem pages.
* This will be moved to the block layer in 2.5.
@@ -203,17 +216,72 @@

static inline void bounce_end_io (struct buffer_head *bh, int uptodate)
{
+ struct page *page;
struct buffer_head *bh_orig = (struct buffer_head *)(bh->b_private);
+ unsigned long flags;

bh_orig->b_end_io(bh_orig, uptodate);
- __free_page(bh->b_page);
+
+ page = bh->b_page;
+
+ spin_lock_irqsave(&emergency_lock, flags);
+ if (nr_emergency_pages >= POOL_SIZE)
+ __free_page(page);
+ else {
+ /*
+ * We are abusing page->list to manage
+ * the highmem emergency pool:
+ */
+ list_add(&page->list, &emergency_pages);
+ nr_emergency_pages++;
+ }
+
+ if (nr_emergency_bhs >= POOL_SIZE) {
#ifdef HIGHMEM_DEBUG
- /* Don't clobber the constructed slab cache */
- init_waitqueue_head(&bh->b_wait);
+ /* Don't clobber the constructed slab cache */
+ init_waitqueue_head(&bh->b_wait);
#endif
- kmem_cache_free(bh_cachep, bh);
+ kmem_cache_free(bh_cachep, bh);
+ } else {
+ /*
+ * Ditto in the bh case, here we abuse b_inode_buffers:
+ */
+ list_add(&bh->b_inode_buffers, &emergency_bhs);
+ nr_emergency_bhs++;
+ }
+ spin_unlock_irqrestore(&emergency_lock, flags);
}

+static __init int init_emergency_pool(void)
+{
+ spin_lock_irq(&emergency_lock);
+ while (nr_emergency_pages < POOL_SIZE) {
+ struct page * page = alloc_page(GFP_ATOMIC);
+ if (!page) {
+ printk("couldn't refill highmem emergency pages");
+ break;
+ }
+ list_add(&page->list, &emergency_pages);
+ nr_emergency_pages++;
+ }
+ while (nr_emergency_bhs < POOL_SIZE) {
+ struct buffer_head * bh = kmem_cache_alloc(bh_cachep, SLAB_ATOMIC);
+ if (!bh) {
+ printk("couldn't refill highmem emergency bhs");
+ break;
+ }
+ list_add(&bh->b_inode_buffers, &emergency_bhs);
+ nr_emergency_bhs++;
+ }
+ spin_unlock_irq(&emergency_lock);
+ printk("allocated %d pages and %d bhs reserved for the highmem bounces\n",
+ nr_emergency_pages, nr_emergency_bhs);
+
+ return 0;
+}
+
+__initcall(init_emergency_pool);
+
static void bounce_end_io_write (struct buffer_head *bh, int uptodate)
{
bounce_end_io(bh, uptodate);
@@ -228,6 +296,82 @@
bounce_end_io(bh, uptodate);
}

+struct page *alloc_bounce_page (void)
+{
+ struct list_head *tmp;
+ struct page *page;
+
+repeat_alloc:
+ page = alloc_page(GFP_BUFFER);
+ if (page)
+ return page;
+ /*
+ * No luck. First, kick the VM so it doesnt idle around while
+ * we are using up our emergency rations.
+ */
+ wakeup_bdflush(0);
+
+ /*
+ * Try to allocate from the emergency pool.
+ */
+ tmp = &emergency_pages;
+ spin_lock_irq(&emergency_lock);
+ if (!list_empty(tmp)) {
+ page = list_entry(tmp->next, struct page, list);
+ list_del(tmp->next);
+ nr_emergency_pages--;
+ }
+ spin_unlock_irq(&emergency_lock);
+ if (page)
+ return page;
+
+ /* we need to wait I/O completion */
+ run_task_queue(&tq_disk);
+
+ current->policy |= SCHED_YIELD;
+ __set_current_state(TASK_RUNNING);
+ schedule();
+ goto repeat_alloc;
+}
+
+struct buffer_head *alloc_bounce_bh (void)
+{
+ struct list_head *tmp;
+ struct buffer_head *bh;
+
+repeat_alloc:
+ bh = kmem_cache_alloc(bh_cachep, SLAB_BUFFER);
+ if (bh)
+ return bh;
+ /*
+ * No luck. First, kick the VM so it doesnt idle around while
+ * we are using up our emergency rations.
+ */
+ wakeup_bdflush(0);
+
+ /*
+ * Try to allocate from the emergency pool.
+ */
+ tmp = &emergency_bhs;
+ spin_lock_irq(&emergency_lock);
+ if (!list_empty(tmp)) {
+ bh = list_entry(tmp->next, struct buffer_head, b_inode_buffers);
+ list_del(tmp->next);
+ nr_emergency_bhs--;
+ }
+ spin_unlock_irq(&emergency_lock);
+ if (bh)
+ return bh;
+
+ /* we need to wait I/O completion */
+ run_task_queue(&tq_disk);
+
+ current->policy |= SCHED_YIELD;
+ __set_current_state(TASK_RUNNING);
+ schedule();
+ goto repeat_alloc;
+}
+
struct buffer_head * create_bounce(int rw, struct buffer_head * bh_orig)
{
struct page *page;
@@ -236,24 +380,15 @@
if (!PageHighMem(bh_orig->b_page))
return bh_orig;

-repeat_bh:
- bh = kmem_cache_alloc(bh_cachep, SLAB_BUFFER);
- if (!bh) {
- wakeup_bdflush(1); /* Sets task->state to TASK_RUNNING */
- goto repeat_bh;
- }
+ bh = alloc_bounce_bh();
/*
* This is wasteful for 1k buffers, but this is a stopgap measure
* and we are being ineffective anyway. This approach simplifies
* things immensly. On boxes with more than 4GB RAM this should
* not be an issue anyway.
*/
-repeat_page:
- page = alloc_page(GFP_BUFFER);
- if (!page) {
- wakeup_bdflush(1); /* Sets task->state to TASK_RUNNING */
- goto repeat_page;
- }
+ page = alloc_bounce_page();
+
set_bh_page(bh, page, 0);

bh->b_next = NULL;

And this one as well to avoid tight loops in getblk without reschedules
in between when normal zone is empty:

diff -urN 2.4.4pre1/fs/buffer.c 2.4.4pre1-blkdev/fs/buffer.c
--- 2.4.4pre1/fs/buffer.c Sun Apr 1 01:17:30 2001
+++ 2.4.4pre1-blkdev/fs/buffer.c Mon Apr 9 15:37:20 2001
@@ -628,7 +622,7 @@
to do in order to release the ramdisk memory is to destroy dirty buffers.

These are two special cases. Normal usage imply the device driver
- to issue a sync on the device (without waiting I/O completation) and
+ to issue a sync on the device (without waiting I/O completion) and
then an invalidate_buffers call that doesn't trash dirty buffers. */
void __invalidate_buffers(kdev_t dev, int destroy_dirty_buffers)
{
@@ -762,7 +756,12 @@
balance_dirty(NODEV);
if (free_shortage())
page_launder(GFP_BUFFER, 0);
- grow_buffers(size);
+ if (!grow_buffers(size)) {
+ wakeup_bdflush(1);
+ current->policy |= SCHED_YIELD;
+ __set_current_state(TASK_RUNNING);
+ schedule();
+ }
}

void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
@@ -1027,12 +1026,13 @@
write_unlock(&hash_table_lock);
spin_unlock(&lru_list_lock);
refill_freelist(size);
+ /* FIXME: getblk should fail if there's no enough memory */
goto repeat;
}

/* -1 -> no need to flush
0 -> async flush
- 1 -> sync flush (wait for I/O completation) */
+ 1 -> sync flush (wait for I/O completion) */
int balance_dirty_state(kdev_t dev)
{
unsigned long dirty, tot, hard_dirty_limit, soft_dirty_limit;
@@ -1431,6 +1431,7 @@
{
struct buffer_head *bh, *head, *tail;

+ /* FIXME: create_buffers should fail if there's no enough memory */
head = create_buffers(page, blocksize, 1);
if (page->buffers)
BUG();
@@ -2367,11 +2368,9 @@
spin_lock(&free_list[index].lock);
tmp = bh;
do {
- struct buffer_head *p = tmp;
-
- tmp = tmp->b_this_page;
- if (buffer_busy(p))
+ if (buffer_busy(tmp))
goto busy_buffer_page;
+ tmp = tmp->b_this_page;
} while (tmp != bh);

spin_lock(&unused_list_lock);
Andrea
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