Re: [PATCH 6/9] f2fs: zstd: Switch to the zstd-1.4.6 API

[Nick Terrell]

> On Sep 15, 2020, at 11:31 PM, Chao Yu <yuchao0@xxxxxxxxxx> wrote:
> 
> Hi Nick,
> 
> remove not related mailing list.
> 
> On 2020/9/16 11:43, Nick Terrell wrote:
>> From: Nick Terrell <terrelln@xxxxxx>
>> Move away from the compatibility wrapper to the zstd-1.4.6 API. This
>> code is more efficient because it uses the single-pass API instead of
>> the streaming API. The streaming API is not necessary because the whole
>> input and output buffers are available. This saves memory because we
>> don't need to allocate a buffer for the window. It is also more
>> efficient because it saves unnecessary memcpy calls.
>> I've had problems testing this code because I see data truncation before
>> and after this patchset. Help testing this patch would be much
>> appreciated.
> 
> Can you please explain more about data truncation? I'm a little confused...
> 
> Do you mean that f2fs doesn't allocate enough memory for zstd compression,
> so that compression is not finished actually, the compressed data is truncated
> at dst buffer?

Hi Chao,

I’ve tested F2FS using a benchmark I adapted from testing BtrFS [0]. It is possible
that the script I’m using is buggy or is exposing an edge case in F2FS. The files
that I copy to F2FS and compress end up truncated with a hole at the end.

It is based off of upstream commit ab29a807a7.

E.g. the end of the copied file looks like this, but the original file has non-zero data
In the end. Until the hole at the end the file is correct.

od dickens | tail -n 5
> 46667760 067502 066167 020056 040440 020163 023511 006555 060412
> 46670000 000000 000000 000000 000000 000000 000000 000000 000000
> *
> 46703060 000000 000000 000000 000000 000000 000000 000000
> 46703076

[0] https://gist.github.com/terrelln/7dd2919937dfbdb8e839e4ad11c81db4

Best,
Nick

> Thanks,
> 
>> Signed-off-by: Nick Terrell <terrelln@xxxxxx>
>> ---
>>  fs/f2fs/compress.c | 102 +++++++++++++++++----------------------------
>>  1 file changed, 38 insertions(+), 64 deletions(-)
>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
>> index e056f3a2b404..b79efce81651 100644
>> --- a/fs/f2fs/compress.c
>> +++ b/fs/f2fs/compress.c
>> @@ -11,7 +11,8 @@
>>  #include <linux/backing-dev.h>
>>  #include <linux/lzo.h>
>>  #include <linux/lz4.h>
>> -#include <linux/zstd_compat.h>
>> +#include <linux/zstd.h>
>> +#include <linux/zstd_errors.h>
>>    #include "f2fs.h"
>>  #include "node.h"
>> @@ -298,21 +299,21 @@ static const struct f2fs_compress_ops f2fs_lz4_ops = {
>>  static int zstd_init_compress_ctx(struct compress_ctx *cc)
>>  {
>>  	ZSTD_parameters params;
>> -	ZSTD_CStream *stream;
>> +	ZSTD_CCtx *ctx;
>>  	void *workspace;
>>  	unsigned int workspace_size;
>>    	params = ZSTD_getParams(F2FS_ZSTD_DEFAULT_CLEVEL, cc->rlen, 0);
>> -	workspace_size = ZSTD_CStreamWorkspaceBound(params.cParams);
>> +	workspace_size = ZSTD_estimateCCtxSize_usingCParams(params.cParams);
>>    	workspace = f2fs_kvmalloc(F2FS_I_SB(cc->inode),
>>  					workspace_size, GFP_NOFS);
>>  	if (!workspace)
>>  		return -ENOMEM;
>>  -	stream = ZSTD_initCStream(params, 0, workspace, workspace_size);
>> -	if (!stream) {
>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_initCStream failed\n",
>> +	ctx = ZSTD_initStaticCCtx(workspace, workspace_size);
>> +	if (!ctx) {
>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_inittaticCStream failed\n",
>>  				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id,
>>  				__func__);
>>  		kvfree(workspace);
>> @@ -320,7 +321,7 @@ static int zstd_init_compress_ctx(struct compress_ctx *cc)
>>  	}
>>    	cc->private = workspace;
>> -	cc->private2 = stream;
>> +	cc->private2 = ctx;
>>    	cc->clen = cc->rlen - PAGE_SIZE - COMPRESS_HEADER_SIZE;
>>  	return 0;
>> @@ -335,65 +336,48 @@ static void zstd_destroy_compress_ctx(struct compress_ctx *cc)
>>    static int zstd_compress_pages(struct compress_ctx *cc)
>>  {
>> -	ZSTD_CStream *stream = cc->private2;
>> -	ZSTD_inBuffer inbuf;
>> -	ZSTD_outBuffer outbuf;
>> -	int src_size = cc->rlen;
>> -	int dst_size = src_size - PAGE_SIZE - COMPRESS_HEADER_SIZE;
>> -	int ret;
>> -
>> -	inbuf.pos = 0;
>> -	inbuf.src = cc->rbuf;
>> -	inbuf.size = src_size;
>> -
>> -	outbuf.pos = 0;
>> -	outbuf.dst = cc->cbuf->cdata;
>> -	outbuf.size = dst_size;
>> -
>> -	ret = ZSTD_compressStream(stream, &outbuf, &inbuf);
>> -	if (ZSTD_isError(ret)) {
>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_compressStream failed, ret: %d\n",
>> -				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id,
>> -				__func__, ZSTD_getErrorCode(ret));
>> -		return -EIO;
>> -	}
>> -
>> -	ret = ZSTD_endStream(stream, &outbuf);
>> +	ZSTD_CCtx *ctx = cc->private2;
>> +	const size_t src_size = cc->rlen;
>> +	const size_t dst_size = src_size - PAGE_SIZE - COMPRESS_HEADER_SIZE;
>> +	ZSTD_parameters params = ZSTD_getParams(F2FS_ZSTD_DEFAULT_CLEVEL, src_size, 0);
>> +	size_t ret;
>> +
>> +	ret = ZSTD_compress_advanced(
>> +			ctx, cc->cbuf->cdata, dst_size, cc->rbuf, src_size, NULL, 0, params);
>>  	if (ZSTD_isError(ret)) {
>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_endStream returned %d\n",
>> +		/*
>> +		 * there is compressed data remained in intermediate buffer due to
>> +		 * no more space in cbuf.cdata
>> +		 */
>> +		if (ZSTD_getErrorCode(ret) == ZSTD_error_dstSize_tooSmall)
>> +			return -EAGAIN;
>> +		/* other compression errors return -EIO */
>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_compress_advanced failed, err: %s\n",
>>  				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id,
>> -				__func__, ZSTD_getErrorCode(ret));
>> +				__func__, ZSTD_getErrorName(ret));
>>  		return -EIO;
>>  	}
>>  -	/*
>> -	 * there is compressed data remained in intermediate buffer due to
>> -	 * no more space in cbuf.cdata
>> -	 */
>> -	if (ret)
>> -		return -EAGAIN;
>> -
>> -	cc->clen = outbuf.pos;
>> +	cc->clen = ret;
>>  	return 0;
>>  }
>>    static int zstd_init_decompress_ctx(struct decompress_io_ctx *dic)
>>  {
>> -	ZSTD_DStream *stream;
>> +	ZSTD_DCtx *ctx;
>>  	void *workspace;
>>  	unsigned int workspace_size;
>>  -	workspace_size = ZSTD_DStreamWorkspaceBound(MAX_COMPRESS_WINDOW_SIZE);
>> +	workspace_size = ZSTD_estimateDCtxSize();
>>    	workspace = f2fs_kvmalloc(F2FS_I_SB(dic->inode),
>>  					workspace_size, GFP_NOFS);
>>  	if (!workspace)
>>  		return -ENOMEM;
>>  -	stream = ZSTD_initDStream(MAX_COMPRESS_WINDOW_SIZE,
>> -					workspace, workspace_size);
>> -	if (!stream) {
>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_initDStream failed\n",
>> +	ctx = ZSTD_initStaticDCtx(workspace, workspace_size);
>> +	if (!ctx) {
>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_initStaticDCtx failed\n",
>>  				KERN_ERR, F2FS_I_SB(dic->inode)->sb->s_id,
>>  				__func__);
>>  		kvfree(workspace);
>> @@ -401,7 +385,7 @@ static int zstd_init_decompress_ctx(struct decompress_io_ctx *dic)
>>  	}
>>    	dic->private = workspace;
>> -	dic->private2 = stream;
>> +	dic->private2 = ctx;
>>    	return 0;
>>  }
>> @@ -415,28 +399,18 @@ static void zstd_destroy_decompress_ctx(struct decompress_io_ctx *dic)
>>    static int zstd_decompress_pages(struct decompress_io_ctx *dic)
>>  {
>> -	ZSTD_DStream *stream = dic->private2;
>> -	ZSTD_inBuffer inbuf;
>> -	ZSTD_outBuffer outbuf;
>> -	int ret;
>> -
>> -	inbuf.pos = 0;
>> -	inbuf.src = dic->cbuf->cdata;
>> -	inbuf.size = dic->clen;
>> -
>> -	outbuf.pos = 0;
>> -	outbuf.dst = dic->rbuf;
>> -	outbuf.size = dic->rlen;
>> +	ZSTD_DCtx *ctx = dic->private2;
>> +	size_t ret;
>>  -	ret = ZSTD_decompressStream(stream, &outbuf, &inbuf);
>> +	ret = ZSTD_decompressDCtx(ctx, dic->rbuf, dic->rlen, dic->cbuf->cdata, dic->clen);
>>  	if (ZSTD_isError(ret)) {
>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_compressStream failed, ret: %d\n",
>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_decompressDCtx failed, err: %s\n",
>>  				KERN_ERR, F2FS_I_SB(dic->inode)->sb->s_id,
>> -				__func__, ZSTD_getErrorCode(ret));
>> +				__func__, ZSTD_getErrorName(ret));
>>  		return -EIO;
>>  	}
>>  -	if (dic->rlen != outbuf.pos) {
>> +	if (dic->rlen != ret) {
>>  		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD invalid rlen:%zu, "
>>  				"expected:%lu\n", KERN_ERR,
>>  				F2FS_I_SB(dic->inode)->sb->s_id,