Date:   Fri, 18 Sep 2020 09:47:32 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Nick Terrell <terrelln@...com>
CC:     Nick Terrell <nickrterrell@...il.com>,
        "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>, Chris Mason <clm@...com>,
        Petr Malat <oss@...at.biz>, Johannes Weiner <jweiner@...com>,
        Niket Agarwal <niketa@...com>, Yann Collet <cyan@...com>
Subject: Re: [PATCH 6/9] f2fs: zstd: Switch to the zstd-1.4.6 API

On 2020/9/18 3:34, Nick Terrell wrote:
> 
> 
>> On Sep 17, 2020, at 11:00 AM, Nick Terrell <terrelln@...com> wrote:
>>
>>
>>
>>> On Sep 16, 2020, at 11:31 PM, Chao Yu <yuchao0@...wei.com> wrote:
>>>
>>> Hi Nick,
>>>
>>> On 2020/9/17 2:39, Nick Terrell wrote:
>>>>> On Sep 15, 2020, at 11:31 PM, Chao Yu <yuchao0@...wei.com> wrote:
>>>>>
>>>>> Hi Nick,
>>>>>
>>>>> remove not related mailing list.
>>>>>
>>>>> On 2020/9/16 11:43, Nick Terrell wrote:
>>>>>> From: Nick Terrell <terrelln@...com>
>>>>>> 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.
>>>
>>> Thanks for your explanation. :)
>>>
>>>> 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
>>>
>>> Shouldn't we just get sha1 value by flitering sha1sum output?
>>>
>>>                asha=`sha1sum $BENCHMARK_DIR/$file |awk {'print $1'}`
>>>                bsha=`sha1sum $MP/$i/$file |awk {'print $1'}`
>>
>> Probably, but it was just a quick one-off script.
> 
> Ah, never mind, you are right.
> 
>>> I can't reproduce this issue by using simple data sample, could you share
>>> that 'dickens' file or other smaller-sized sample if you have?
>>
>> The /tmp/silesia directory in the example is populated with all the files from
>> this website. It is a popular data compression benchmark corpus. You can
>> click on the “total” link to download a zip archive of all the files.
>>
>> http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia
>>
>> -Nick
> 
> I’ve spent some time minimizing the test case. This script [0] is the minimized
> test case that doesn’t require any input files, it builds its own.
> 
> Several observations:
> * The input file needs to be 7700481 bytes large, smaller files don’t trigger the bug.
> * You have to `chattr +c` the file after copying it otherwise the bug doesn’t occur.
> * After `chattr +c` you have to unmount and remount the filesystem to trigger the bug.
> 
> I’ve reproduced on v5.9-rc5 (856deb866d16e). I’ve also reproduced on my host machine
> running 5.8.5-arch1-1.
> 
> [0] https://gist.github.com/terrelln/4bba325abdfa3a6f014e9911ac92a185

Ah, I got it.

Step of enabling compressed inode is not correct, we should touch an empty file, and
then use 'chattr +c' on that file to enable compression, otherwise the race condition
could be complicated to handle. So we need below diff to disallow setting compression
flag on an non-empty file:

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 8a422400e824..b462db7898fd 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1836,6 +1836,8 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
  		if (iflags & F2FS_COMPR_FL) {
  			if (!f2fs_may_compress(inode))
  				return -EINVAL;
+			if (get_dirty_pages(inode) || fi->i_compr_blocks)
+				return  -EINVAL;

  			set_compress_context(inode);
  		}

Could you adjust your script and retest?

touch $DST_FILE
chattr +c $DST_FILE
cp $SRC_FILE $DST_FILE

Thanks,

> 
> Best,
> Nick
> 
>>> Thanks,
>>>
>>>> Best,
>>>> Nick
>>>>> Thanks,
>>>>>
>>>>>> Signed-off-by: Nick Terrell <terrelln@...com>
>>>>>> ---
>>>>>> 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,
> 

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