Re: [PATCH v2 5/8] staging: erofs: introduce generic decompression backend

[Chao Yu]

On 2019/6/21 18:42, Gao Xiang wrote:
> Hi Chao,
> 
> On 2019/6/21 17:46, Chao Yu wrote:
>> On 2019/6/21 0:07, Gao Xiang wrote:
>>> This patch adds a new generic decompression framework
>>> in order to replace the old LZ4-specific decompression code.
>>>
>>> Even though LZ4 is still the only supported algorithm, yet
>>> it is more cleaner and easy to integrate new algorithm than
>>> the old almost hard-coded decompression backend.
>>>
>>> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
>>> ---
>>>  drivers/staging/erofs/Makefile       |   2 +-
>>>  drivers/staging/erofs/compress.h     |  21 ++
>>>  drivers/staging/erofs/decompressor.c | 307 +++++++++++++++++++++++++++
>>>  3 files changed, 329 insertions(+), 1 deletion(-)
>>>  create mode 100644 drivers/staging/erofs/decompressor.c
>>>
>>> diff --git a/drivers/staging/erofs/Makefile b/drivers/staging/erofs/Makefile
>>> index 84b412c7a991..adeb5d6e2668 100644
>>> --- a/drivers/staging/erofs/Makefile
>>> +++ b/drivers/staging/erofs/Makefile
>>> @@ -9,5 +9,5 @@ obj-$(CONFIG_EROFS_FS) += erofs.o
>>>  ccflags-y += -I $(srctree)/$(src)/include
>>>  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) += unzip_vle.o unzip_vle_lz4.o zmap.o
>>> +erofs-$(CONFIG_EROFS_FS_ZIP) += unzip_vle.o unzip_vle_lz4.o zmap.o decompressor.o
>>>  
>>> diff --git a/drivers/staging/erofs/compress.h b/drivers/staging/erofs/compress.h
>>> index 1dcfc3b35118..ebeccb1f4eae 100644
>>> --- a/drivers/staging/erofs/compress.h
>>> +++ b/drivers/staging/erofs/compress.h
>>> @@ -9,6 +9,24 @@
>>>  #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 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
>>> @@ -36,5 +54,8 @@ static inline bool z_erofs_put_stagingpage(struct list_head *pagepool,
>>>  	return true;
>>>  }
>>>  
>>> +int z_erofs_decompress(struct z_erofs_decompress_req *rq,
>>> +		       struct list_head *pagepool);
>>> +
>>>  #endif
>>>  
>>> diff --git a/drivers/staging/erofs/decompressor.c b/drivers/staging/erofs/decompressor.c
>>> new file mode 100644
>>> index 000000000000..c68d17b579e0
>>> --- /dev/null
>>> +++ b/drivers/staging/erofs/decompressor.c
>>> @@ -0,0 +1,307 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * linux/drivers/staging/erofs/decompressor.c
>>> + *
>>> + * Copyright (C) 2019 HUAWEI, Inc.
>>> + *             http://www.huawei.com/
>>> + * Created by Gao Xiang <gaoxiang25@xxxxxxxxxx>
>>> + */
>>> +#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)
>>> +
>>> +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 unused[DIV_ROUND_UP(LZ4_MAX_DISTANCE_PAGES,
>>> +					  BITS_PER_LONG)] = { 0 };
>>> +	void *kaddr = NULL;
>>> +	unsigned int i, j, k;
>>> +
>>> +	for (i = 0; i < nr; ++i) {
>>> +		struct page *const page = rq->out[i];
>>> +
>>> +		j = i & (LZ4_MAX_DISTANCE_PAGES - 1);
>>> +		if (availables[j])
>>> +			__set_bit(j, unused);
>>> +
>>> +		if (page) {
>>> +			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;
>>> +
>>> +		k = find_first_bit(unused, LZ4_MAX_DISTANCE_PAGES);
>>> +		if (k < LZ4_MAX_DISTANCE_PAGES) {
>>> +			j = k;
>>> +			get_page(availables[j]);
>>> +		} else {
>>> +			DBG_BUGON(availables[j]);
>>> +
>>> +			if (!list_empty(pagepool)) {
>>> +				availables[j] = lru_to_page(pagepool);
>>> +				list_del(&availables[j]->lru);
>>> +				DBG_BUGON(page_ref_count(availables[j]) != 1);
>>> +			} else {
>>> +				availables[j] = alloc_pages(GFP_KERNEL, 0);
>>> +				if (!availables[j])
>>> +					return -ENOMEM;
>>> +			}
>>> +			availables[j]->mapping = Z_EROFS_MAPPING_STAGING;
>>
>> Could we use __stagingpage_alloc() instead opened codes, there is something
>> different in between them though.
> 
> It was written "on propose" since the problem is that currently __stagingpage_alloc()
> will allocate all pages in GFP_NOFAIL case, but memory allocation failure is accepted
> here, therefore I open code to aim at introducing new decompression backend.
> 
> I will submit another patch after this series to clean up all staging page allocation
> cases later, which was already on my scheduling list. :)

Hi Xiang,

Yes, I noticed that there is something different in between __stagingpage_alloc
and opened codes, I think we can change __stagingpage_alloc to accept extra
parameters for different requirement.

But, anyway, I agreed with you that we can clean up with additional patch later. :)

Thanks,

> 
> Thanks,
> Gao Xiang
> 
>>
>> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
>>
>> Thanks,
>>
>>> +		}
>>> +		rq->out[i] = availables[j];
>>> +		__clear_bit(j, unused);
>>> +	}
>>> +	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;
>>> +	while (!src[inputmargin & ~PAGE_MASK])
>>> +		if (!(++inputmargin & ~PAGE_MASK))
>>> +			break;
>>> +
>>> +	if (inputmargin >= rq->inputsize) {
>>> +		kunmap_atomic(src);
>>> +		return -EIO;
>>> +	}
>>> +
>>> +	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);
>>> +
>>> +		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);
>>> +}
>>> +
>>>
> .
>