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bdi: Add bdi->id

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There currently is no way to universally identify and lookup a bdi
without holding a reference and pointer to it.  This patch adds an
non-recycling bdi->id and implements bdi_get_by_id() which looks up
bdis by their ids.  This will be used by memcg foreign inode flushing.

I left bdi_list alone for simplicity and because while rb_tree does
support rcu assignment it doesn't seem to guarantee lossless walk when
walk is racing aginst tree rebalance operations.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2019-08-26 09:06:53 -07:00 committed by Jens Axboe
parent 5b9cce4c7e
commit 34f8fe501f
3 changed files with 66 additions and 2 deletions
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2
include/linux/backing-dev-defs.h
View File

@ -185,6 +185,8 @@ struct bdi_writeback {
};
struct backing_dev_info {
u64 id;
struct rb_node rb_node; /* keyed by ->id */
struct list_head bdi_list;
unsigned long ra_pages; /* max readahead in PAGE_SIZE units */
unsigned long io_pages; /* max allowed IO size */

1
include/linux/backing-dev.h
View File

@ -24,6 +24,7 @@ static inline struct backing_dev_info *bdi_get(struct backing_dev_info *bdi)
return bdi;
}
struct backing_dev_info *bdi_get_by_id(u64 id);
void bdi_put(struct backing_dev_info *bdi);
__printf(2, 3)

65
mm/backing-dev.c
View File

@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/wait.h>
#include <linux/rbtree.h>
#include <linux/backing-dev.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
@ -22,10 +23,12 @@ EXPORT_SYMBOL_GPL(noop_backing_dev_info);
static struct class *bdi_class;
/*
* bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
* locking.
* bdi_lock protects bdi_tree and updates to bdi_list. bdi_list has RCU
* reader side locking.
*/
DEFINE_SPINLOCK(bdi_lock);
static u64 bdi_id_cursor;
static struct rb_root bdi_tree = RB_ROOT;
LIST_HEAD(bdi_list);
/* bdi_wq serves all asynchronous writeback tasks */
@ -859,9 +862,58 @@ struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id)
}
EXPORT_SYMBOL(bdi_alloc_node);
static struct rb_node **bdi_lookup_rb_node(u64 id, struct rb_node **parentp)
{
struct rb_node **p = &bdi_tree.rb_node;
struct rb_node *parent = NULL;
struct backing_dev_info *bdi;
lockdep_assert_held(&bdi_lock);
while (*p) {
parent = *p;
bdi = rb_entry(parent, struct backing_dev_info, rb_node);
if (bdi->id > id)
p = &(*p)->rb_left;
else if (bdi->id < id)
p = &(*p)->rb_right;
else
break;
}
if (parentp)
*parentp = parent;
return p;
}
/**
* bdi_get_by_id - lookup and get bdi from its id
* @id: bdi id to lookup
*
* Find bdi matching @id and get it. Returns NULL if the matching bdi
* doesn't exist or is already unregistered.
*/
struct backing_dev_info *bdi_get_by_id(u64 id)
{
struct backing_dev_info *bdi = NULL;
struct rb_node **p;
spin_lock_bh(&bdi_lock);
p = bdi_lookup_rb_node(id, NULL);
if (*p) {
bdi = rb_entry(*p, struct backing_dev_info, rb_node);
bdi_get(bdi);
}
spin_unlock_bh(&bdi_lock);
return bdi;
}
int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
{
struct device *dev;
struct rb_node *parent, **p;
if (bdi->dev) /* The driver needs to use separate queues per device */
return 0;
@ -877,7 +929,15 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
set_bit(WB_registered, &bdi->wb.state);
spin_lock_bh(&bdi_lock);
bdi->id = ++bdi_id_cursor;
p = bdi_lookup_rb_node(bdi->id, &parent);
rb_link_node(&bdi->rb_node, parent, p);
rb_insert_color(&bdi->rb_node, &bdi_tree);
list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
spin_unlock_bh(&bdi_lock);
trace_writeback_bdi_register(bdi);
@ -918,6 +978,7 @@ EXPORT_SYMBOL(bdi_register_owner);
static void bdi_remove_from_list(struct backing_dev_info *bdi)
{
spin_lock_bh(&bdi_lock);
rb_erase(&bdi->rb_node, &bdi_tree);
list_del_rcu(&bdi->bdi_list);
spin_unlock_bh(&bdi_lock);