1 files changed, 703 insertions, 0 deletions

diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
new file mode 100644
index 000000000..35a0224d4
--- /dev/null
+++ b/fs/btrfs/zstd.c
@@ -0,0 +1,703 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ */
+
+#include <linux/bio.h>
+#include <linux/bitmap.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/sched/mm.h>
+#include <linux/pagemap.h>
+#include <linux/refcount.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/zstd.h>
+#include "misc.h"
+#include "compression.h"
+#include "ctree.h"
+
+#define ZSTD_BTRFS_MAX_WINDOWLOG 17
+#define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
+#define ZSTD_BTRFS_DEFAULT_LEVEL 3
+#define ZSTD_BTRFS_MAX_LEVEL 15
+/* 307s to avoid pathologically clashing with transaction commit */
+#define ZSTD_BTRFS_RECLAIM_JIFFIES (307 * HZ)
+
+static zstd_parameters zstd_get_btrfs_parameters(unsigned int level,
+						 size_t src_len)
+{
+	zstd_parameters params = zstd_get_params(level, src_len);
+
+	if (params.cParams.windowLog > ZSTD_BTRFS_MAX_WINDOWLOG)
+		params.cParams.windowLog = ZSTD_BTRFS_MAX_WINDOWLOG;
+	WARN_ON(src_len > ZSTD_BTRFS_MAX_INPUT);
+	return params;
+}
+
+struct workspace {
+	void *mem;
+	size_t size;
+	char *buf;
+	unsigned int level;
+	unsigned int req_level;
+	unsigned long last_used; /* jiffies */
+	struct list_head list;
+	struct list_head lru_list;
+	zstd_in_buffer in_buf;
+	zstd_out_buffer out_buf;
+};
+
+/*
+ * Zstd Workspace Management
+ *
+ * Zstd workspaces have different memory requirements depending on the level.
+ * The zstd workspaces are managed by having individual lists for each level
+ * and a global lru.  Forward progress is maintained by protecting a max level
+ * workspace.
+ *
+ * Getting a workspace is done by using the bitmap to identify the levels that
+ * have available workspaces and scans up.  This lets us recycle higher level
+ * workspaces because of the monotonic memory guarantee.  A workspace's
+ * last_used is only updated if it is being used by the corresponding memory
+ * level.  Putting a workspace involves adding it back to the appropriate places
+ * and adding it back to the lru if necessary.
+ *
+ * A timer is used to reclaim workspaces if they have not been used for
+ * ZSTD_BTRFS_RECLAIM_JIFFIES.  This helps keep only active workspaces around.
+ * The upper bound is provided by the workqueue limit which is 2 (percpu limit).
+ */
+
+struct zstd_workspace_manager {
+	const struct btrfs_compress_op *ops;
+	spinlock_t lock;
+	struct list_head lru_list;
+	struct list_head idle_ws[ZSTD_BTRFS_MAX_LEVEL];
+	unsigned long active_map;
+	wait_queue_head_t wait;
+	struct timer_list timer;
+};
+
+static struct zstd_workspace_manager wsm;
+
+static size_t zstd_ws_mem_sizes[ZSTD_BTRFS_MAX_LEVEL];
+
+static inline struct workspace *list_to_workspace(struct list_head *list)
+{
+	return container_of(list, struct workspace, list);
+}
+
+void zstd_free_workspace(struct list_head *ws);
+struct list_head *zstd_alloc_workspace(unsigned int level);
+
+/**
+ * Timer callback to free unused workspaces.
+ *
+ * @t: timer
+ *
+ * This scans the lru_list and attempts to reclaim any workspace that hasn't
+ * been used for ZSTD_BTRFS_RECLAIM_JIFFIES.
+ *
+ * The context is softirq and does not need the _bh locking primitives.
+ */
+static void zstd_reclaim_timer_fn(struct timer_list *timer)
+{
+	unsigned long reclaim_threshold = jiffies - ZSTD_BTRFS_RECLAIM_JIFFIES;
+	struct list_head *pos, *next;
+
+	spin_lock(&wsm.lock);
+
+	if (list_empty(&wsm.lru_list)) {
+		spin_unlock(&wsm.lock);
+		return;
+	}
+
+	list_for_each_prev_safe(pos, next, &wsm.lru_list) {
+		struct workspace *victim = container_of(pos, struct workspace,
+							lru_list);
+		unsigned int level;
+
+		if (time_after(victim->last_used, reclaim_threshold))
+			break;
+
+		/* workspace is in use */
+		if (victim->req_level)
+			continue;
+
+		level = victim->level;
+		list_del(&victim->lru_list);
+		list_del(&victim->list);
+		zstd_free_workspace(&victim->list);
+
+		if (list_empty(&wsm.idle_ws[level - 1]))
+			clear_bit(level - 1, &wsm.active_map);
+
+	}
+
+	if (!list_empty(&wsm.lru_list))
+		mod_timer(&wsm.timer, jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);
+
+	spin_unlock(&wsm.lock);
+}
+
+/*
+ * zstd_calc_ws_mem_sizes - calculate monotonic memory bounds
+ *
+ * It is possible based on the level configurations that a higher level
+ * workspace uses less memory than a lower level workspace.  In order to reuse
+ * workspaces, this must be made a monotonic relationship.  This precomputes
+ * the required memory for each level and enforces the monotonicity between
+ * level and memory required.
+ */
+static void zstd_calc_ws_mem_sizes(void)
+{
+	size_t max_size = 0;
+	unsigned int level;
+
+	for (level = 1; level <= ZSTD_BTRFS_MAX_LEVEL; level++) {
+		zstd_parameters params =
+			zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
+		size_t level_size =
+			max_t(size_t,
+			      zstd_cstream_workspace_bound(&params.cParams),
+			      zstd_dstream_workspace_bound(ZSTD_BTRFS_MAX_INPUT));
+
+		max_size = max_t(size_t, max_size, level_size);
+		zstd_ws_mem_sizes[level - 1] = max_size;
+	}
+}
+
+void zstd_init_workspace_manager(void)
+{
+	struct list_head *ws;
+	int i;
+
+	zstd_calc_ws_mem_sizes();
+
+	wsm.ops = &btrfs_zstd_compress;
+	spin_lock_init(&wsm.lock);
+	init_waitqueue_head(&wsm.wait);
+	timer_setup(&wsm.timer, zstd_reclaim_timer_fn, 0);
+
+	INIT_LIST_HEAD(&wsm.lru_list);
+	for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++)
+		INIT_LIST_HEAD(&wsm.idle_ws[i]);
+
+	ws = zstd_alloc_workspace(ZSTD_BTRFS_MAX_LEVEL);
+	if (IS_ERR(ws)) {
+		pr_warn(
+		"BTRFS: cannot preallocate zstd compression workspace\n");
+	} else {
+		set_bit(ZSTD_BTRFS_MAX_LEVEL - 1, &wsm.active_map);
+		list_add(ws, &wsm.idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1]);
+	}
+}
+
+void zstd_cleanup_workspace_manager(void)
+{
+	struct workspace *workspace;
+	int i;
+
+	spin_lock_bh(&wsm.lock);
+	for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++) {
+		while (!list_empty(&wsm.idle_ws[i])) {
+			workspace = container_of(wsm.idle_ws[i].next,
+						 struct workspace, list);
+			list_del(&workspace->list);
+			list_del(&workspace->lru_list);
+			zstd_free_workspace(&workspace->list);
+		}
+	}
+	spin_unlock_bh(&wsm.lock);
+
+	del_timer_sync(&wsm.timer);
+}
+
+/*
+ * zstd_find_workspace - find workspace
+ * @level: compression level
+ *
+ * This iterates over the set bits in the active_map beginning at the requested
+ * compression level.  This lets us utilize already allocated workspaces before
+ * allocating a new one.  If the workspace is of a larger size, it is used, but
+ * the place in the lru_list and last_used times are not updated.  This is to
+ * offer the opportunity to reclaim the workspace in favor of allocating an
+ * appropriately sized one in the future.
+ */
+static struct list_head *zstd_find_workspace(unsigned int level)
+{
+	struct list_head *ws;
+	struct workspace *workspace;
+	int i = level - 1;
+
+	spin_lock_bh(&wsm.lock);
+	for_each_set_bit_from(i, &wsm.active_map, ZSTD_BTRFS_MAX_LEVEL) {
+		if (!list_empty(&wsm.idle_ws[i])) {
+			ws = wsm.idle_ws[i].next;
+			workspace = list_to_workspace(ws);
+			list_del_init(ws);
+			/* keep its place if it's a lower level using this */
+			workspace->req_level = level;
+			if (level == workspace->level)
+				list_del(&workspace->lru_list);
+			if (list_empty(&wsm.idle_ws[i]))
+				clear_bit(i, &wsm.active_map);
+			spin_unlock_bh(&wsm.lock);
+			return ws;
+		}
+	}
+	spin_unlock_bh(&wsm.lock);
+
+	return NULL;
+}
+
+/*
+ * zstd_get_workspace - zstd's get_workspace
+ * @level: compression level
+ *
+ * If @level is 0, then any compression level can be used.  Therefore, we begin
+ * scanning from 1.  We first scan through possible workspaces and then after
+ * attempt to allocate a new workspace.  If we fail to allocate one due to
+ * memory pressure, go to sleep waiting for the max level workspace to free up.
+ */
+struct list_head *zstd_get_workspace(unsigned int level)
+{
+	struct list_head *ws;
+	unsigned int nofs_flag;
+
+	/* level == 0 means we can use any workspace */
+	if (!level)
+		level = 1;
+
+again:
+	ws = zstd_find_workspace(level);
+	if (ws)
+		return ws;
+
+	nofs_flag = memalloc_nofs_save();
+	ws = zstd_alloc_workspace(level);
+	memalloc_nofs_restore(nofs_flag);
+
+	if (IS_ERR(ws)) {
+		DEFINE_WAIT(wait);
+
+		prepare_to_wait(&wsm.wait, &wait, TASK_UNINTERRUPTIBLE);
+		schedule();
+		finish_wait(&wsm.wait, &wait);
+
+		goto again;
+	}
+
+	return ws;
+}
+
+/*
+ * zstd_put_workspace - zstd put_workspace
+ * @ws: list_head for the workspace
+ *
+ * When putting back a workspace, we only need to update the LRU if we are of
+ * the requested compression level.  Here is where we continue to protect the
+ * max level workspace or update last_used accordingly.  If the reclaim timer
+ * isn't set, it is also set here.  Only the max level workspace tries and wakes
+ * up waiting workspaces.
+ */
+void zstd_put_workspace(struct list_head *ws)
+{
+	struct workspace *workspace = list_to_workspace(ws);
+
+	spin_lock_bh(&wsm.lock);
+
+	/* A node is only taken off the lru if we are the corresponding level */
+	if (workspace->req_level == workspace->level) {
+		/* Hide a max level workspace from reclaim */
+		if (list_empty(&wsm.idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1])) {
+			INIT_LIST_HEAD(&workspace->lru_list);
+		} else {
+			workspace->last_used = jiffies;
+			list_add(&workspace->lru_list, &wsm.lru_list);
+			if (!timer_pending(&wsm.timer))
+				mod_timer(&wsm.timer,
+					  jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);
+		}
+	}
+
+	set_bit(workspace->level - 1, &wsm.active_map);
+	list_add(&workspace->list, &wsm.idle_ws[workspace->level - 1]);
+	workspace->req_level = 0;
+
+	spin_unlock_bh(&wsm.lock);
+
+	if (workspace->level == ZSTD_BTRFS_MAX_LEVEL)
+		cond_wake_up(&wsm.wait);
+}
+
+void zstd_free_workspace(struct list_head *ws)
+{
+	struct workspace *workspace = list_entry(ws, struct workspace, list);
+
+	kvfree(workspace->mem);
+	kfree(workspace->buf);
+	kfree(workspace);
+}
+
+struct list_head *zstd_alloc_workspace(unsigned int level)
+{
+	struct workspace *workspace;
+
+	workspace = kzalloc(sizeof(*workspace), GFP_KERNEL);
+	if (!workspace)
+		return ERR_PTR(-ENOMEM);
+
+	workspace->size = zstd_ws_mem_sizes[level - 1];
+	workspace->level = level;
+	workspace->req_level = level;
+	workspace->last_used = jiffies;
+	workspace->mem = kvmalloc(workspace->size, GFP_KERNEL);
+	workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!workspace->mem || !workspace->buf)
+		goto fail;
+
+	INIT_LIST_HEAD(&workspace->list);
+	INIT_LIST_HEAD(&workspace->lru_list);
+
+	return &workspace->list;
+fail:
+	zstd_free_workspace(&workspace->list);
+	return ERR_PTR(-ENOMEM);
+}
+
+int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
+		u64 start, struct page **pages, unsigned long *out_pages,
+		unsigned long *total_in, unsigned long *total_out)
+{
+	struct workspace *workspace = list_entry(ws, struct workspace, list);
+	zstd_cstream *stream;
+	int ret = 0;
+	int nr_pages = 0;
+	struct page *in_page = NULL;  /* The current page to read */
+	struct page *out_page = NULL; /* The current page to write to */
+	unsigned long tot_in = 0;
+	unsigned long tot_out = 0;
+	unsigned long len = *total_out;
+	const unsigned long nr_dest_pages = *out_pages;
+	unsigned long max_out = nr_dest_pages * PAGE_SIZE;
+	zstd_parameters params = zstd_get_btrfs_parameters(workspace->req_level,
+							   len);
+
+	*out_pages = 0;
+	*total_out = 0;
+	*total_in = 0;
+
+	/* Initialize the stream */
+	stream = zstd_init_cstream(&params, len, workspace->mem,
+			workspace->size);
+	if (!stream) {
+		pr_warn("BTRFS: zstd_init_cstream failed\n");
+		ret = -EIO;
+		goto out;
+	}
+
+	/* map in the first page of input data */
+	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+	workspace->in_buf.src = kmap_local_page(in_page);
+	workspace->in_buf.pos = 0;
+	workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
+
+
+	/* Allocate and map in the output buffer */
+	out_page = alloc_page(GFP_NOFS);
+	if (out_page == NULL) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	pages[nr_pages++] = out_page;
+	workspace->out_buf.dst = page_address(out_page);
+	workspace->out_buf.pos = 0;
+	workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
+
+	while (1) {
+		size_t ret2;
+
+		ret2 = zstd_compress_stream(stream, &workspace->out_buf,
+				&workspace->in_buf);
+		if (zstd_is_error(ret2)) {
+			pr_debug("BTRFS: zstd_compress_stream returned %d\n",
+					zstd_get_error_code(ret2));
+			ret = -EIO;
+			goto out;
+		}
+
+		/* Check to see if we are making it bigger */
+		if (tot_in + workspace->in_buf.pos > 8192 &&
+				tot_in + workspace->in_buf.pos <
+				tot_out + workspace->out_buf.pos) {
+			ret = -E2BIG;
+			goto out;
+		}
+
+		/* We've reached the end of our output range */
+		if (workspace->out_buf.pos >= max_out) {
+			tot_out += workspace->out_buf.pos;
+			ret = -E2BIG;
+			goto out;
+		}
+
+		/* Check if we need more output space */
+		if (workspace->out_buf.pos == workspace->out_buf.size) {
+			tot_out += PAGE_SIZE;
+			max_out -= PAGE_SIZE;
+			if (nr_pages == nr_dest_pages) {
+				ret = -E2BIG;
+				goto out;
+			}
+			out_page = alloc_page(GFP_NOFS);
+			if (out_page == NULL) {
+				ret = -ENOMEM;
+				goto out;
+			}
+			pages[nr_pages++] = out_page;
+			workspace->out_buf.dst = page_address(out_page);
+			workspace->out_buf.pos = 0;
+			workspace->out_buf.size = min_t(size_t, max_out,
+							PAGE_SIZE);
+		}
+
+		/* We've reached the end of the input */
+		if (workspace->in_buf.pos >= len) {
+			tot_in += workspace->in_buf.pos;
+			break;
+		}
+
+		/* Check if we need more input */
+		if (workspace->in_buf.pos == workspace->in_buf.size) {
+			tot_in += PAGE_SIZE;
+			kunmap_local(workspace->in_buf.src);
+			put_page(in_page);
+			start += PAGE_SIZE;
+			len -= PAGE_SIZE;
+			in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+			workspace->in_buf.src = kmap_local_page(in_page);
+			workspace->in_buf.pos = 0;
+			workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
+		}
+	}
+	while (1) {
+		size_t ret2;
+
+		ret2 = zstd_end_stream(stream, &workspace->out_buf);
+		if (zstd_is_error(ret2)) {
+			pr_debug("BTRFS: zstd_end_stream returned %d\n",
+					zstd_get_error_code(ret2));
+			ret = -EIO;
+			goto out;
+		}
+		if (ret2 == 0) {
+			tot_out += workspace->out_buf.pos;
+			break;
+		}
+		if (workspace->out_buf.pos >= max_out) {
+			tot_out += workspace->out_buf.pos;
+			ret = -E2BIG;
+			goto out;
+		}
+
+		tot_out += PAGE_SIZE;
+		max_out -= PAGE_SIZE;
+		if (nr_pages == nr_dest_pages) {
+			ret = -E2BIG;
+			goto out;
+		}
+		out_page = alloc_page(GFP_NOFS);
+		if (out_page == NULL) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		pages[nr_pages++] = out_page;
+		workspace->out_buf.dst = page_address(out_page);
+		workspace->out_buf.pos = 0;
+		workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
+	}
+
+	if (tot_out >= tot_in) {
+		ret = -E2BIG;
+		goto out;
+	}
+
+	ret = 0;
+	*total_in = tot_in;
+	*total_out = tot_out;
+out:
+	*out_pages = nr_pages;
+	if (workspace->in_buf.src) {
+		kunmap_local(workspace->in_buf.src);
+		put_page(in_page);
+	}
+	return ret;
+}
+
+int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
+{
+	struct workspace *workspace = list_entry(ws, struct workspace, list);
+	struct page **pages_in = cb->compressed_pages;
+	size_t srclen = cb->compressed_len;
+	zstd_dstream *stream;
+	int ret = 0;
+	unsigned long page_in_index = 0;
+	unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_SIZE);
+	unsigned long buf_start;
+	unsigned long total_out = 0;
+
+	stream = zstd_init_dstream(
+			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
+	if (!stream) {
+		pr_debug("BTRFS: zstd_init_dstream failed\n");
+		ret = -EIO;
+		goto done;
+	}
+
+	workspace->in_buf.src = kmap_local_page(pages_in[page_in_index]);
+	workspace->in_buf.pos = 0;
+	workspace->in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
+
+	workspace->out_buf.dst = workspace->buf;
+	workspace->out_buf.pos = 0;
+	workspace->out_buf.size = PAGE_SIZE;
+
+	while (1) {
+		size_t ret2;
+
+		ret2 = zstd_decompress_stream(stream, &workspace->out_buf,
+				&workspace->in_buf);
+		if (zstd_is_error(ret2)) {
+			pr_debug("BTRFS: zstd_decompress_stream returned %d\n",
+					zstd_get_error_code(ret2));
+			ret = -EIO;
+			goto done;
+		}
+		buf_start = total_out;
+		total_out += workspace->out_buf.pos;
+		workspace->out_buf.pos = 0;
+
+		ret = btrfs_decompress_buf2page(workspace->out_buf.dst,
+				total_out - buf_start, cb, buf_start);
+		if (ret == 0)
+			break;
+
+		if (workspace->in_buf.pos >= srclen)
+			break;
+
+		/* Check if we've hit the end of a frame */
+		if (ret2 == 0)
+			break;
+
+		if (workspace->in_buf.pos == workspace->in_buf.size) {
+			kunmap_local(workspace->in_buf.src);
+			page_in_index++;
+			if (page_in_index >= total_pages_in) {
+				workspace->in_buf.src = NULL;
+				ret = -EIO;
+				goto done;
+			}
+			srclen -= PAGE_SIZE;
+			workspace->in_buf.src = kmap_local_page(pages_in[page_in_index]);
+			workspace->in_buf.pos = 0;
+			workspace->in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
+		}
+	}
+	ret = 0;
+	zero_fill_bio(cb->orig_bio);
+done:
+	if (workspace->in_buf.src)
+		kunmap_local(workspace->in_buf.src);
+	return ret;
+}
+
+int zstd_decompress(struct list_head *ws, unsigned char *data_in,
+		struct page *dest_page, unsigned long start_byte, size_t srclen,
+		size_t destlen)
+{
+	struct workspace *workspace = list_entry(ws, struct workspace, list);
+	zstd_dstream *stream;
+	int ret = 0;
+	size_t ret2;
+	unsigned long total_out = 0;
+	unsigned long pg_offset = 0;
+
+	stream = zstd_init_dstream(
+			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
+	if (!stream) {
+		pr_warn("BTRFS: zstd_init_dstream failed\n");
+		ret = -EIO;
+		goto finish;
+	}
+
+	destlen = min_t(size_t, destlen, PAGE_SIZE);
+
+	workspace->in_buf.src = data_in;
+	workspace->in_buf.pos = 0;
+	workspace->in_buf.size = srclen;
+
+	workspace->out_buf.dst = workspace->buf;
+	workspace->out_buf.pos = 0;
+	workspace->out_buf.size = PAGE_SIZE;
+
+	ret2 = 1;
+	while (pg_offset < destlen
+	       && workspace->in_buf.pos < workspace->in_buf.size) {
+		unsigned long buf_start;
+		unsigned long buf_offset;
+		unsigned long bytes;
+
+		/* Check if the frame is over and we still need more input */
+		if (ret2 == 0) {
+			pr_debug("BTRFS: zstd_decompress_stream ended early\n");
+			ret = -EIO;
+			goto finish;
+		}
+		ret2 = zstd_decompress_stream(stream, &workspace->out_buf,
+				&workspace->in_buf);
+		if (zstd_is_error(ret2)) {
+			pr_debug("BTRFS: zstd_decompress_stream returned %d\n",
+					zstd_get_error_code(ret2));
+			ret = -EIO;
+			goto finish;
+		}
+
+		buf_start = total_out;
+		total_out += workspace->out_buf.pos;
+		workspace->out_buf.pos = 0;
+
+		if (total_out <= start_byte)
+			continue;
+
+		if (total_out > start_byte && buf_start < start_byte)
+			buf_offset = start_byte - buf_start;
+		else
+			buf_offset = 0;
+
+		bytes = min_t(unsigned long, destlen - pg_offset,
+				workspace->out_buf.size - buf_offset);
+
+		memcpy_to_page(dest_page, pg_offset,
+			       workspace->out_buf.dst + buf_offset, bytes);
+
+		pg_offset += bytes;
+	}
+	ret = 0;
+finish:
+	if (pg_offset < destlen) {
+		memzero_page(dest_page, pg_offset, destlen - pg_offset);
+	}
+	return ret;
+}
+
+const struct btrfs_compress_op btrfs_zstd_compress = {
+	/* ZSTD uses own workspace manager */
+	.workspace_manager = NULL,
+	.max_level	= ZSTD_BTRFS_MAX_LEVEL,
+	.default_level	= ZSTD_BTRFS_DEFAULT_LEVEL,
+};