https://github.com/torvalds/linux
Revision 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 authored by Filipe Manana on 19 November 2015, 11:45:48 UTC, committed by Chris Mason on 25 November 2015, 13:22:08 UTC
Currently scrub can race with the cleaner kthread when the later attempts to delete an unused block group, and the result is preventing the cleaner kthread from ever deleting later the block group - unless the block group becomes used and unused again. The following diagram illustrates that race: CPU 1 CPU 2 cleaner kthread btrfs_delete_unused_bgs() gets block group X from fs_info->unused_bgs and removes it from that list scrub_enumerate_chunks() searches device tree using its commit root finds device extent for block group X gets block group X from the tree fs_info->block_group_cache_tree (via btrfs_lookup_block_group()) sets bg X to RO sees the block group is already RO and therefore doesn't delete it nor adds it back to unused list So fix this by making scrub add the block group again to the list of unused block groups if the block group is still unused when it finished scrubbing it and it hasn't been removed already. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
1 parent 020d5b7
Tip revision: 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 authored by Filipe Manana on 19 November 2015, 11:45:48 UTC
Btrfs: fix scrub preventing unused block groups from being deleted
Btrfs: fix scrub preventing unused block groups from being deleted
Tip revision: 758f2df
quicklist.c
/*
* Quicklist support.
*
* Quicklists are light weight lists of pages that have a defined state
* on alloc and free. Pages must be in the quicklist specific defined state
* (zero by default) when the page is freed. It seems that the initial idea
* for such lists first came from Dave Miller and then various other people
* improved on it.
*
* Copyright (C) 2007 SGI,
* Christoph Lameter <clameter@sgi.com>
* Generalized, added support for multiple lists and
* constructors / destructors.
*/
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/mmzone.h>
#include <linux/quicklist.h>
DEFINE_PER_CPU(struct quicklist [CONFIG_NR_QUICK], quicklist);
#define FRACTION_OF_NODE_MEM 16
static unsigned long max_pages(unsigned long min_pages)
{
unsigned long node_free_pages, max;
int node = numa_node_id();
struct zone *zones = NODE_DATA(node)->node_zones;
int num_cpus_on_node;
node_free_pages =
#ifdef CONFIG_ZONE_DMA
zone_page_state(&zones[ZONE_DMA], NR_FREE_PAGES) +
#endif
#ifdef CONFIG_ZONE_DMA32
zone_page_state(&zones[ZONE_DMA32], NR_FREE_PAGES) +
#endif
zone_page_state(&zones[ZONE_NORMAL], NR_FREE_PAGES);
max = node_free_pages / FRACTION_OF_NODE_MEM;
num_cpus_on_node = cpumask_weight(cpumask_of_node(node));
max /= num_cpus_on_node;
return max(max, min_pages);
}
static long min_pages_to_free(struct quicklist *q,
unsigned long min_pages, long max_free)
{
long pages_to_free;
pages_to_free = q->nr_pages - max_pages(min_pages);
return min(pages_to_free, max_free);
}
/*
* Trim down the number of pages in the quicklist
*/
void quicklist_trim(int nr, void (*dtor)(void *),
unsigned long min_pages, unsigned long max_free)
{
long pages_to_free;
struct quicklist *q;
q = &get_cpu_var(quicklist)[nr];
if (q->nr_pages > min_pages) {
pages_to_free = min_pages_to_free(q, min_pages, max_free);
while (pages_to_free > 0) {
/*
* We pass a gfp_t of 0 to quicklist_alloc here
* because we will never call into the page allocator.
*/
void *p = quicklist_alloc(nr, 0, NULL);
if (dtor)
dtor(p);
free_page((unsigned long)p);
pages_to_free--;
}
}
put_cpu_var(quicklist);
}
unsigned long quicklist_total_size(void)
{
unsigned long count = 0;
int cpu;
struct quicklist *ql, *q;
for_each_online_cpu(cpu) {
ql = per_cpu(quicklist, cpu);
for (q = ql; q < ql + CONFIG_NR_QUICK; q++)
count += q->nr_pages;
}
return count;
}
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