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Revision c4f675cd40d955d539180506c09515c90169b15b authored by Sergei Trofimovich on 20 May 2011, 20:20:30 UTC, committed by Chris Mason on 23 May 2011, 17:24:14 UTC 
btrfs: don't spin in shrink_delalloc if there is nothing to free
 
Observed as a large delay when --mixed filesystem is filled up.
Test example:
1. create tiny --mixed FS:
   $ dd if=/dev/zero of=2G.img seek=$((2048 * 1024 * 1024 - 1)) count=1 bs=1
   $ mkfs.btrfs --mixed 2G.img
   $ mount -oloop 2G.img /mnt/ut/
2. Try to fill it up:
   $ dd if=/dev/urandom of=10M.file bs=10240 count=1024
   $ seq 1 256 | while read file_no; do echo $file_no; time cp 10M.file ${file_no}.copy; done

Up to '200.copy' it goes fast, but when disk fills-up each -ENOSPC
message takes 3 seconds to pop-up _every_ ENOSPC (and in usermode linux
it's even more: 30-60 seconds!). (Maybe, time depends on kernel's timer resolution).

No IO, no CPU load, just rescheduling. Some debugging revealed busy spinning
in shrink_delalloc.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
1 parent 0f3b708
Raw File
prio_heap.c 
/*
 * Simple insertion-only static-sized priority heap containing
 * pointers, based on CLR, chapter 7
 */

#include <linux/slab.h>
#include <linux/prio_heap.h>

int heap_init(struct ptr_heap *heap, size_t size, gfp_t gfp_mask,
	      int (*gt)(void *, void *))
{
	heap->ptrs = kmalloc(size, gfp_mask);
	if (!heap->ptrs)
		return -ENOMEM;
	heap->size = 0;
	heap->max = size / sizeof(void *);
	heap->gt = gt;
	return 0;
}

void heap_free(struct ptr_heap *heap)
{
	kfree(heap->ptrs);
}

void *heap_insert(struct ptr_heap *heap, void *p)
{
	void *res;
	void **ptrs = heap->ptrs;
	int pos;

	if (heap->size < heap->max) {
		/* Heap insertion */
		pos = heap->size++;
		while (pos > 0 && heap->gt(p, ptrs[(pos-1)/2])) {
			ptrs[pos] = ptrs[(pos-1)/2];
			pos = (pos-1)/2;
		}
		ptrs[pos] = p;
		return NULL;
	}

	/* The heap is full, so something will have to be dropped */

	/* If the new pointer is greater than the current max, drop it */
	if (heap->gt(p, ptrs[0]))
		return p;

	/* Replace the current max and heapify */
	res = ptrs[0];
	ptrs[0] = p;
	pos = 0;

	while (1) {
		int left = 2 * pos + 1;
		int right = 2 * pos + 2;
		int largest = pos;
		if (left < heap->size && heap->gt(ptrs[left], p))
			largest = left;
		if (right < heap->size && heap->gt(ptrs[right], ptrs[largest]))
			largest = right;
		if (largest == pos)
			break;
		/* Push p down the heap one level and bump one up */
		ptrs[pos] = ptrs[largest];
		ptrs[largest] = p;
		pos = largest;
	}
	return res;
}
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