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erofs: support adjust lz4 history window size 

lz4 uses LZ4_DISTANCE_MAX to record history preservation. When
using rolling decompression, a block with a higher compression
ratio will cause a larger memory allocation (up to 64k). It may
cause a large resource burden in extreme cases on devices with
small memory and a large number of concurrent IOs. So appropriately
reducing this value can improve performance.

Decreasing this value will reduce the compression ratio (except
when input_size <LZ4_DISTANCE_MAX). But considering that erofs
currently only supports 4k output, reducing this value will not
significantly reduce the compression benefits.

The maximum value of LZ4_DISTANCE_MAX defined by lz4 is 64k, and
we can only reduce this value. For the old kernel, it just can't
reduce the memory allocation during rolling decompression without
affecting the decompression result.

Link: https://lore.kernel.org/r/20210329012308.28743-3-hsiangkao@aol.com
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
[ Gao Xiang: introduce struct erofs_sb_lz4_info for configurations. ]
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
This commit is contained in:
Huang Jianan 2021-03-29 09:23:06 +08:00 committed by Gao Xiang
parent de06a6a375
commit 5d50538fc5
4 changed files with 42 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
fs/erofs/decompressor.c
View File

@ -28,6 +28,17 @@ struct z_erofs_decompressor {
char *name;
};
int z_erofs_load_lz4_config(struct super_block *sb,
struct erofs_super_block *dsb)
{
u16 distance = le16_to_cpu(dsb->lz4_max_distance);
EROFS_SB(sb)->lz4.max_distance_pages = distance ?
DIV_ROUND_UP(distance, PAGE_SIZE) + 1 :
LZ4_MAX_DISTANCE_PAGES;
return 0;
}
static int z_erofs_lz4_prepare_destpages(struct z_erofs_decompress_req *rq,
struct list_head *pagepool)
{
@ -36,6 +47,8 @@ static int z_erofs_lz4_prepare_destpages(struct z_erofs_decompress_req *rq,
struct page *availables[LZ4_MAX_DISTANCE_PAGES] = { NULL };
unsigned long bounced[DIV_ROUND_UP(LZ4_MAX_DISTANCE_PAGES,
BITS_PER_LONG)] = { 0 };
unsigned int lz4_max_distance_pages =
EROFS_SB(rq->sb)->lz4.max_distance_pages;
void *kaddr = NULL;
unsigned int i, j, top;
@ -44,14 +57,14 @@ static int z_erofs_lz4_prepare_destpages(struct z_erofs_decompress_req *rq,
struct page *const page = rq->out[i];
struct page *victim;
if (j >= LZ4_MAX_DISTANCE_PAGES)
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];
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) {

4
fs/erofs/erofs_fs.h
View File

@ -39,7 +39,9 @@ struct erofs_super_block {
__u8 uuid[16]; /* 128-bit uuid for volume */
__u8 volume_name[16]; /* volume name */
__le32 feature_incompat;
__u8 reserved2[44];
/* customized lz4 sliding window size instead of 64k by default */
__le16 lz4_max_distance;
__u8 reserved2[42];
};
/*

19
fs/erofs/internal.h
View File

@ -59,6 +59,12 @@ struct erofs_fs_context {
unsigned int mount_opt;
};
/* all filesystem-wide lz4 configurations */
struct erofs_sb_lz4_info {
/* # of pages needed for EROFS lz4 rolling decompression */
u16 max_distance_pages;
};
struct erofs_sb_info {
#ifdef CONFIG_EROFS_FS_ZIP
/* list for all registered superblocks, mainly for shrinker */
@ -72,6 +78,8 @@ struct erofs_sb_info {
/* pseudo inode to manage cached pages */
struct inode *managed_cache;
struct erofs_sb_lz4_info lz4;
#endif /* CONFIG_EROFS_FS_ZIP */
u32 blocks;
u32 meta_blkaddr;
@ -430,6 +438,8 @@ int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
struct erofs_workgroup *egrp);
int erofs_try_to_free_cached_page(struct address_space *mapping,
struct page *page);
int z_erofs_load_lz4_config(struct super_block *sb,
struct erofs_super_block *dsb);
#else
static inline void erofs_shrinker_register(struct super_block *sb) {}
static inline void erofs_shrinker_unregister(struct super_block *sb) {}
@ -437,6 +447,15 @@ static inline int erofs_init_shrinker(void) { return 0; }
static inline void erofs_exit_shrinker(void) {}
static inline int z_erofs_init_zip_subsystem(void) { return 0; }
static inline void z_erofs_exit_zip_subsystem(void) {}
static inline int z_erofs_load_lz4_config(struct super_block *sb,
struct erofs_super_block *dsb)
{
if (dsb->lz4_max_distance) {
erofs_err(sb, "lz4 algorithm isn't enabled");
return -EINVAL;
}
return 0;
}
#endif /* !CONFIG_EROFS_FS_ZIP */
#define EFSCORRUPTED EUCLEAN /* Filesystem is corrupted */

4
fs/erofs/super.c
View File

@ -187,7 +187,9 @@ static int erofs_read_superblock(struct super_block *sb)
ret = -EFSCORRUPTED;
goto out;
}
ret = 0;
/* parse on-disk compression configurations */
ret = z_erofs_load_lz4_config(sb, dsb);
out:
kunmap(page);
put_page(page);