linux/drivers/md/dm-cache-background-tracker.c
Joe Thornber 64748b1645 dm cache background tracker: limit amount of background work that may be issued at once
On large systems the cache policy can be over enthusiastic and queue far
too much dirty data to be written back.  This consumes memory.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2017-11-10 15:45:03 -05:00

250 lines
5.0 KiB
C

/*
* Copyright (C) 2017 Red Hat. All rights reserved.
*
* This file is released under the GPL.
*/
#include "dm-cache-background-tracker.h"
/*----------------------------------------------------------------*/
#define DM_MSG_PREFIX "dm-background-tracker"
struct bt_work {
struct list_head list;
struct rb_node node;
struct policy_work work;
};
struct background_tracker {
unsigned max_work;
atomic_t pending_promotes;
atomic_t pending_writebacks;
atomic_t pending_demotes;
struct list_head issued;
struct list_head queued;
struct rb_root pending;
struct kmem_cache *work_cache;
};
struct background_tracker *btracker_create(unsigned max_work)
{
struct background_tracker *b = kmalloc(sizeof(*b), GFP_KERNEL);
if (!b) {
DMERR("couldn't create background_tracker");
return NULL;
}
b->max_work = max_work;
atomic_set(&b->pending_promotes, 0);
atomic_set(&b->pending_writebacks, 0);
atomic_set(&b->pending_demotes, 0);
INIT_LIST_HEAD(&b->issued);
INIT_LIST_HEAD(&b->queued);
b->pending = RB_ROOT;
b->work_cache = KMEM_CACHE(bt_work, 0);
if (!b->work_cache) {
DMERR("couldn't create mempool for background work items");
kfree(b);
b = NULL;
}
return b;
}
EXPORT_SYMBOL_GPL(btracker_create);
void btracker_destroy(struct background_tracker *b)
{
kmem_cache_destroy(b->work_cache);
kfree(b);
}
EXPORT_SYMBOL_GPL(btracker_destroy);
static int cmp_oblock(dm_oblock_t lhs, dm_oblock_t rhs)
{
if (from_oblock(lhs) < from_oblock(rhs))
return -1;
if (from_oblock(rhs) < from_oblock(lhs))
return 1;
return 0;
}
static bool __insert_pending(struct background_tracker *b,
struct bt_work *nw)
{
int cmp;
struct bt_work *w;
struct rb_node **new = &b->pending.rb_node, *parent = NULL;
while (*new) {
w = container_of(*new, struct bt_work, node);
parent = *new;
cmp = cmp_oblock(w->work.oblock, nw->work.oblock);
if (cmp < 0)
new = &((*new)->rb_left);
else if (cmp > 0)
new = &((*new)->rb_right);
else
/* already present */
return false;
}
rb_link_node(&nw->node, parent, new);
rb_insert_color(&nw->node, &b->pending);
return true;
}
static struct bt_work *__find_pending(struct background_tracker *b,
dm_oblock_t oblock)
{
int cmp;
struct bt_work *w;
struct rb_node **new = &b->pending.rb_node;
while (*new) {
w = container_of(*new, struct bt_work, node);
cmp = cmp_oblock(w->work.oblock, oblock);
if (cmp < 0)
new = &((*new)->rb_left);
else if (cmp > 0)
new = &((*new)->rb_right);
else
break;
}
return *new ? w : NULL;
}
static void update_stats(struct background_tracker *b, struct policy_work *w, int delta)
{
switch (w->op) {
case POLICY_PROMOTE:
atomic_add(delta, &b->pending_promotes);
break;
case POLICY_DEMOTE:
atomic_add(delta, &b->pending_demotes);
break;
case POLICY_WRITEBACK:
atomic_add(delta, &b->pending_writebacks);
break;
}
}
unsigned btracker_nr_writebacks_queued(struct background_tracker *b)
{
return atomic_read(&b->pending_writebacks);
}
EXPORT_SYMBOL_GPL(btracker_nr_writebacks_queued);
unsigned btracker_nr_demotions_queued(struct background_tracker *b)
{
return atomic_read(&b->pending_demotes);
}
EXPORT_SYMBOL_GPL(btracker_nr_demotions_queued);
static bool max_work_reached(struct background_tracker *b)
{
return atomic_read(&b->pending_promotes) +
atomic_read(&b->pending_writebacks) +
atomic_read(&b->pending_demotes) >= b->max_work;
}
struct bt_work *alloc_work(struct background_tracker *b)
{
if (max_work_reached(b))
return NULL;
return kmem_cache_alloc(b->work_cache, GFP_NOWAIT);
}
int btracker_queue(struct background_tracker *b,
struct policy_work *work,
struct policy_work **pwork)
{
struct bt_work *w;
if (pwork)
*pwork = NULL;
w = alloc_work(b);
if (!w)
return -ENOMEM;
memcpy(&w->work, work, sizeof(*work));
if (!__insert_pending(b, w)) {
/*
* There was a race, we'll just ignore this second
* bit of work for the same oblock.
*/
kmem_cache_free(b->work_cache, w);
return -EINVAL;
}
if (pwork) {
*pwork = &w->work;
list_add(&w->list, &b->issued);
} else
list_add(&w->list, &b->queued);
update_stats(b, &w->work, 1);
return 0;
}
EXPORT_SYMBOL_GPL(btracker_queue);
/*
* Returns -ENODATA if there's no work.
*/
int btracker_issue(struct background_tracker *b, struct policy_work **work)
{
struct bt_work *w;
if (list_empty(&b->queued))
return -ENODATA;
w = list_first_entry(&b->queued, struct bt_work, list);
list_move(&w->list, &b->issued);
*work = &w->work;
return 0;
}
EXPORT_SYMBOL_GPL(btracker_issue);
void btracker_complete(struct background_tracker *b,
struct policy_work *op)
{
struct bt_work *w = container_of(op, struct bt_work, work);
update_stats(b, &w->work, -1);
rb_erase(&w->node, &b->pending);
list_del(&w->list);
kmem_cache_free(b->work_cache, w);
}
EXPORT_SYMBOL_GPL(btracker_complete);
bool btracker_promotion_already_present(struct background_tracker *b,
dm_oblock_t oblock)
{
return __find_pending(b, oblock) != NULL;
}
EXPORT_SYMBOL_GPL(btracker_promotion_already_present);
/*----------------------------------------------------------------*/