[PATCH v3 20/24] erofs: introduce generic decompression backend

Gao Xiang
2019-07-22T02:51:34Z

This patch adds decompression backend to EROFS, which
supports uncompressed and LZ4 compressed data.

For compressed data, it uses the following strategy:
1) If outputsize is very small (totally less than a threshold),
decompress to the per-CPU buffer and do memcpy directly
in order to avoid vmap() overhead;
2) Otherwise it will fill bounced pages if needed and vmap
all output pages into a continuous virtual memory area,
memcpy compressed data to the per-CPU buffer for inplace
I/O [1] and decompress.

Since LZ4 is a lz77-based algorithm which has a dynamically
populated ("sliding window") dictionary and the maximum
lookback distance is 65535. Therefore the number of bounced
pages could be limited by erofs based on this property.

[1] `LZ4 decompression inplace' will eliminate the extra memcpy
if iend - oend margin is safe enough, see the following patch.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
fs/erofs/Kconfig | 10 ++
fs/erofs/Makefile | 2 +-
fs/erofs/compress.h | 89 ++++++++++++
fs/erofs/decompressor.c | 301 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 401 insertions(+), 1 deletion(-)
create mode 100644 fs/erofs/compress.h
create mode 100644 fs/erofs/decompressor.c

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 19d11cf45480..25fa020bd6a4 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -80,6 +80,16 @@ config EROFS_FS_SECURITY

If you are not using a security module, say N.

+config EROFS_FS_USE_VM_MAP_RAM
+ bool "EROFS VM_MAP_RAM Support"
+ depends on EROFS_FS
+ default y
+ help
+ use vm_map_ram / vm_unmap_ram pair which have better performance
+ instead of vmap/vunmap pair.
+
+ If you don't know what these are, say Y.
+
config EROFS_FS_ZIP
bool "EROFS Data Compression Support"
depends on EROFS_FS
diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
index 6a63c5998980..afb7c6556bf9 100644
--- a/fs/erofs/Makefile
+++ b/fs/erofs/Makefile
@@ -7,5 +7,5 @@ ccflags-y += -DEROFS_VERSION=\"$(EROFS_VERSION)\"
obj-$(CONFIG_EROFS_FS) += erofs.o
erofs-objs := super.o inode.o data.o namei.o dir.o utils.o
erofs-$(CONFIG_EROFS_FS_XATTR) += xattr.o
-erofs-$(CONFIG_EROFS_FS_ZIP) += zmap.o
+erofs-$(CONFIG_EROFS_FS_ZIP) += decompressor.o zmap.o

diff --git a/fs/erofs/compress.h b/fs/erofs/compress.h
new file mode 100644
index 000000000000..dbcac48ac888
--- /dev/null
+++ b/fs/erofs/compress.h
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * linux/fs/erofs/compress.h
+ *
+ * Copyright (C) 2019 HUAWEI, Inc.
+ * http://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ */
+#ifndef __EROFS_FS_COMPRESS_H
+#define __EROFS_FS_COMPRESS_H
+
+#include "internal.h"
+
+enum {
+ Z_EROFS_COMPRESSION_SHIFTED = Z_EROFS_COMPRESSION_MAX,
+ Z_EROFS_COMPRESSION_RUNTIME_MAX
+};
+
+struct z_erofs_decompress_req {
+ struct super_block *sb;
+ struct page **in, **out;
+
+ unsigned short pageofs_out;
+ unsigned int inputsize, outputsize;
+
+ /* indicate the algorithm will be used for decompression */
+ unsigned int alg;
+ bool inplace_io, partial_decoding;
+};
+
+/*
+ * - 0x5A110C8D ('sallocated', Z_EROFS_MAPPING_STAGING) -
+ * used to mark temporary allocated pages from other
+ * file/cached pages and NULL mapping pages.
+ */
+#define Z_EROFS_MAPPING_STAGING ((void *)0x5A110C8D)
+
+/* check if a page is marked as staging */
+static inline bool z_erofs_page_is_staging(struct page *page)
+{
+ return page->mapping == Z_EROFS_MAPPING_STAGING;
+}
+
+static inline bool z_erofs_put_stagingpage(struct list_head *pagepool,
+ struct page *page)
+{
+ if (!z_erofs_page_is_staging(page))
+ return false;
+
+ /* staging pages should not be used by others at the same time */
+ if (page_ref_count(page) > 1)
+ put_page(page);
+ else
+ list_add(&page->lru, pagepool);
+ return true;
+}
+
+static inline void *erofs_vmap(struct page **pages, unsigned int count)
+{
+#ifdef CONFIG_EROFS_FS_USE_VM_MAP_RAM
+ int i = 0;
+
+ while (1) {
+ void *addr = vm_map_ram(pages, count, -1, PAGE_KERNEL);
+ /* retry two more times (totally 3 times) */
+ if (addr || ++i >= 3)
+ return addr;
+ vm_unmap_aliases();
+ }
+ return NULL;
+#else
+ return vmap(pages, count, VM_MAP, PAGE_KERNEL);
+#endif
+}
+
+static inline void erofs_vunmap(const void *mem, unsigned int count)
+{
+#ifdef CONFIG_EROFS_FS_USE_VM_MAP_RAM
+ vm_unmap_ram(mem, count);
+#else
+ vunmap(mem);
+#endif
+}
+
+int z_erofs_decompress(struct z_erofs_decompress_req *rq,
+ struct list_head *pagepool);
+
+#endif
+
diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
new file mode 100644
index 000000000000..2ee10bb7e440
--- /dev/null
+++ b/fs/erofs/decompressor.c
@@ -0,0 +1,301 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/erofs/decompressor.c
+ *
+ * Copyright (C) 2019 HUAWEI, Inc.
+ * http://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ */
+#include "compress.h"
+#include <linux/lz4.h>
+
+#ifndef LZ4_DISTANCE_MAX /* history window size */
+#define LZ4_DISTANCE_MAX 65535 /* set to maximum value by default */
+#endif
+
+#define LZ4_MAX_DISTANCE_PAGES (DIV_ROUND_UP(LZ4_DISTANCE_MAX, PAGE_SIZE) + 1)
+
+struct z_erofs_decompressor {
+ /*
+ * if destpages have sparsed pages, fill them with bounce pages.
+ * it also check whether destpages indicate continuous physical memory.
+ */
+ int (*prepare_destpages)(struct z_erofs_decompress_req *rq,
+ struct list_head *pagepool);
+ int (*decompress)(struct z_erofs_decompress_req *rq, u8 *out);
+ char *name;
+};
+
+static int lz4_prepare_destpages(struct z_erofs_decompress_req *rq,
+ struct list_head *pagepool)
+{
+ const unsigned int nr =
+ PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
+ struct page *availables[LZ4_MAX_DISTANCE_PAGES] = { NULL };
+ unsigned long bounced[DIV_ROUND_UP(LZ4_MAX_DISTANCE_PAGES,
+ BITS_PER_LONG)] = { 0 };
+ void *kaddr = NULL;
+ unsigned int i, j, top;
+
+ top = 0;
+ for (i = j = 0; i < nr; ++i, ++j) {
+ struct page *const page = rq->out[i];
+ struct page *victim;
+
+ if (j >= LZ4_MAX_DISTANCE_PAGES)
+ j = 0;
+
+ /* 'valid' bounced can only be tested after a complete round */
+ if (test_bit(j, bounced)) {
+ DBG_BUGON(i < LZ4_MAX_DISTANCE_PAGES);
+ DBG_BUGON(top >= LZ4_MAX_DISTANCE_PAGES);
+ availables[top++] = rq->out[i - LZ4_MAX_DISTANCE_PAGES];
+ }
+
+ if (page) {
+ __clear_bit(j, bounced);
+ if (kaddr) {
+ if (kaddr + PAGE_SIZE == page_address(page))
+ kaddr += PAGE_SIZE;
+ else
+ kaddr = NULL;
+ } else if (!i) {
+ kaddr = page_address(page);
+ }
+ continue;
+ }
+ kaddr = NULL;
+ __set_bit(j, bounced);
+
+ if (top) {
+ victim = availables[--top];
+ get_page(victim);
+ } else {
+ victim = erofs_allocpage(pagepool, GFP_KERNEL, false);
+ if (unlikely(!victim))
+ return -ENOMEM;
+ victim->mapping = Z_EROFS_MAPPING_STAGING;
+ }
+ rq->out[i] = victim;
+ }
+ return kaddr ? 1 : 0;
+}
+
+static void *generic_copy_inplace_data(struct z_erofs_decompress_req *rq,
+ u8 *src, unsigned int pageofs_in)
+{
+ /*
+ * if in-place decompression is ongoing, those decompressed
+ * pages should be copied in order to avoid being overlapped.
+ */
+ struct page **in = rq->in;
+ u8 *const tmp = erofs_get_pcpubuf(0);
+ u8 *tmpp = tmp;
+ unsigned int inlen = rq->inputsize - pageofs_in;
+ unsigned int count = min_t(uint, inlen, PAGE_SIZE - pageofs_in);
+
+ while (tmpp < tmp + inlen) {
+ if (!src)
+ src = kmap_atomic(*in);
+ memcpy(tmpp, src + pageofs_in, count);
+ kunmap_atomic(src);
+ src = NULL;
+ tmpp += count;
+ pageofs_in = 0;
+ count = PAGE_SIZE;
+ ++in;
+ }
+ return tmp;
+}
+
+static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
+{
+ unsigned int inputmargin, inlen;
+ u8 *src;
+ bool copied;
+ int ret;
+
+ if (rq->inputsize > PAGE_SIZE)
+ return -ENOTSUPP;
+
+ src = kmap_atomic(*rq->in);
+ inputmargin = 0;
+
+ copied = false;
+ inlen = rq->inputsize - inputmargin;
+ if (rq->inplace_io) {
+ src = generic_copy_inplace_data(rq, src, inputmargin);
+ inputmargin = 0;
+ copied = true;
+ }
+
+ ret = LZ4_decompress_safe_partial(src + inputmargin, out,
+ inlen, rq->outputsize,
+ rq->outputsize);
+ if (ret < 0) {
+ errln("%s, failed to decompress, in[%p, %u, %u] out[%p, %u]",
+ __func__, src + inputmargin, inlen, inputmargin,
+ out, rq->outputsize);
+ WARN_ON(1);
+ print_hex_dump(KERN_DEBUG, "[ in]: ", DUMP_PREFIX_OFFSET,
+ 16, 1, src + inputmargin, inlen, true);
+ print_hex_dump(KERN_DEBUG, "[out]: ", DUMP_PREFIX_OFFSET,
+ 16, 1, out, rq->outputsize, true);
+ ret = -EIO;
+ }
+
+ if (copied)
+ erofs_put_pcpubuf(src);
+ else
+ kunmap_atomic(src);
+ return ret;
+}
+
+static struct z_erofs_decompressor decompressors[] = {
+ [Z_EROFS_COMPRESSION_SHIFTED] = {
+ .name = "shifted"
+ },
+ [Z_EROFS_COMPRESSION_LZ4] = {
+ .prepare_destpages = lz4_prepare_destpages,
+ .decompress = lz4_decompress,
+ .name = "lz4"
+ },
+};
+
+static void copy_from_pcpubuf(struct page **out, const char *dst,
+ unsigned short pageofs_out,
+ unsigned int outputsize)
+{
+ const char *end = dst + outputsize;
+ const unsigned int righthalf = PAGE_SIZE - pageofs_out;
+ const char *cur = dst - pageofs_out;
+
+ while (cur < end) {
+ struct page *const page = *out++;
+
+ if (page) {
+ char *buf = kmap_atomic(page);
+
+ if (cur >= dst) {
+ memcpy(buf, cur, min_t(uint, PAGE_SIZE,
+ end - cur));
+ } else {
+ memcpy(buf + pageofs_out, cur + pageofs_out,
+ min_t(uint, righthalf, end - cur));
+ }
+ kunmap_atomic(buf);
+ }
+ cur += PAGE_SIZE;
+ }
+}
+
+static int decompress_generic(struct z_erofs_decompress_req *rq,
+ struct list_head *pagepool)
+{
+ const unsigned int nrpages_out =
+ PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
+ const struct z_erofs_decompressor *alg = decompressors + rq->alg;
+ unsigned int dst_maptype;
+ void *dst;
+ int ret;
+
+ if (nrpages_out == 1 && !rq->inplace_io) {
+ DBG_BUGON(!*rq->out);
+ dst = kmap_atomic(*rq->out);
+ dst_maptype = 0;
+ goto dstmap_out;
+ }
+
+ /*
+ * For the case of small output size (especially much less
+ * than PAGE_SIZE), memcpy the decompressed data rather than
+ * compressed data is preferred.
+ */
+ if (rq->outputsize <= PAGE_SIZE * 7 / 8) {
+ dst = erofs_get_pcpubuf(0);
+ if (IS_ERR(dst))
+ return PTR_ERR(dst);
+
+ rq->inplace_io = false;
+ ret = alg->decompress(rq, dst);
+ if (!ret)
+ copy_from_pcpubuf(rq->out, dst, rq->pageofs_out,
+ rq->outputsize);
+
+ erofs_put_pcpubuf(dst);
+ return ret;
+ }
+
+ ret = alg->prepare_destpages(rq, pagepool);
+ if (ret < 0) {
+ return ret;
+ } else if (ret) {
+ dst = page_address(*rq->out);
+ dst_maptype = 1;
+ goto dstmap_out;
+ }
+
+ dst = erofs_vmap(rq->out, nrpages_out);
+ if (!dst)
+ return -ENOMEM;
+ dst_maptype = 2;
+
+dstmap_out:
+ ret = alg->decompress(rq, dst + rq->pageofs_out);
+
+ if (!dst_maptype)
+ kunmap_atomic(dst);
+ else if (dst_maptype == 2)
+ erofs_vunmap(dst, nrpages_out);
+ return ret;
+}
+
+static int shifted_decompress(const struct z_erofs_decompress_req *rq,
+ struct list_head *pagepool)
+{
+ const unsigned int nrpages_out =
+ PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
+ const unsigned int righthalf = PAGE_SIZE - rq->pageofs_out;
+ unsigned char *src, *dst;
+
+ if (nrpages_out > 2) {
+ DBG_BUGON(1);
+ return -EIO;
+ }
+
+ if (rq->out[0] == *rq->in) {
+ DBG_BUGON(nrpages_out != 1);
+ return 0;
+ }
+
+ src = kmap_atomic(*rq->in);
+ if (!rq->out[0]) {
+ dst = NULL;
+ } else {
+ dst = kmap_atomic(rq->out[0]);
+ memcpy(dst + rq->pageofs_out, src, righthalf);
+ }
+
+ if (rq->out[1] == *rq->in) {
+ memmove(src, src + righthalf, rq->pageofs_out);
+ } else if (nrpages_out == 2) {
+ if (dst)
+ kunmap_atomic(dst);
+ DBG_BUGON(!rq->out[1]);
+ dst = kmap_atomic(rq->out[1]);
+ memcpy(dst, src + righthalf, rq->pageofs_out);
+ }
+ if (dst)
+ kunmap_atomic(dst);
+ kunmap_atomic(src);
+ return 0;
+}
+
+int z_erofs_decompress(struct z_erofs_decompress_req *rq,
+ struct list_head *pagepool)
+{
+ if (rq->alg == Z_EROFS_COMPRESSION_SHIFTED)
+ return shifted_decompress(rq, pagepool);
+ return decompress_generic(rq, pagepool);
+}
+
--
2.17.1