path: root/fs/fuse/dax.c

// SPDX-License-Identifier: GPL-2.0
/*
 * dax: direct host memory access
 * Copyright (C) 2020 Red Hat, Inc.
 */

#include "fuse_i.h"

#include <linux/delay.h>
#include <linux/dax.h>
#include <linux/uio.h>
#include <linux/pagemap.h>
#include <linux/pfn_t.h>
#include <linux/iomap.h>
#include <linux/interval_tree.h>

/*
 * Default memory range size.  A power of 2 so it agrees with common FUSE_INIT
 * map_alignment values 4KB and 64KB.
 */
#define FUSE_DAX_SHIFT	21
#define FUSE_DAX_SZ	(1 << FUSE_DAX_SHIFT)
#define FUSE_DAX_PAGES	(FUSE_DAX_SZ / PAGE_SIZE)

/* Number of ranges reclaimer will try to free in one invocation */
#define FUSE_DAX_RECLAIM_CHUNK		(10)

/*
 * Dax memory reclaim threshold in percetage of total ranges. When free
 * number of free ranges drops below this threshold, reclaim can trigger
 * Default is 20%
 */
#define FUSE_DAX_RECLAIM_THRESHOLD	(20)

/** Translation information for file offsets to DAX window offsets */
struct fuse_dax_mapping {
	/* Pointer to inode where this memory range is mapped */
	struct inode *inode;

	/* Will connect in fcd->free_ranges to keep track of free memory */
	struct list_head list;

	/* For interval tree in file/inode */
	struct interval_tree_node itn;

	/* Will connect in fc->busy_ranges to keep track busy memory */
	struct list_head busy_list;

	/** Position in DAX window */
	u64 window_offset;

	/** Length of mapping, in bytes */
	loff_t length;

	/* Is this mapping read-only or read-write */
	bool writable;

	/* reference count when the mapping is used by dax iomap. */
	refcount_t refcnt;
};

/* Per-inode dax map */
struct fuse_inode_dax {
	/* Semaphore to protect modifications to the dmap tree */
	struct rw_semaphore sem;

	/* Sorted rb tree of struct fuse_dax_mapping elements */
	struct rb_root_cached tree;
	unsigned long nr;
};

struct fuse_conn_dax {
	/* DAX device */
	struct dax_device *dev;

	/* Lock protecting accessess to  members of this structure */
	spinlock_t lock;

	/* List of memory ranges which are busy */
	unsigned long nr_busy_ranges;
	struct list_head busy_ranges;

	/* Worker to free up memory ranges */
	struct delayed_work free_work;

	/* Wait queue for a dax range to become free */
	wait_queue_head_t range_waitq;

	/* DAX Window Free Ranges */
	long nr_free_ranges;
	struct list_head free_ranges;

	unsigned long nr_ranges;
};

static inline struct fuse_dax_mapping *
node_to_dmap(struct interval_tree_node *node)
{
	if (!node)
		return NULL;

	return