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Subject[PATCH] erofs: support adjust lz4 history window size
Date
From: huangjianan <huangjianan@oppo.com>

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.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
---
fs/erofs/decompressor.c | 13 +++++++++----
fs/erofs/erofs_fs.h | 3 ++-
fs/erofs/internal.h | 3 +++
fs/erofs/super.c | 3 +++
4 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 1cb1ffd10569..94ae56b3ff71 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -36,22 +36,27 @@ 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_distance_pages = LZ4_MAX_DISTANCE_PAGES;
void *kaddr = NULL;
unsigned int i, j, top;

+ if (EROFS_SB(rq->sb)->compr_alg)
+ lz4_distance_pages = DIV_ROUND_UP(EROFS_SB(rq->sb)->compr_alg,
+ PAGE_SIZE) + 1;
+
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)
+ if (j >= lz4_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_distance_pages);
+ DBG_BUGON(top >= lz4_distance_pages);
+ availables[top++] = rq->out[i - lz4_distance_pages];
}

if (page) {
diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
index 9ad1615f4474..bffc02991f5a 100644
--- a/fs/erofs/erofs_fs.h
+++ b/fs/erofs/erofs_fs.h
@@ -39,7 +39,8 @@ struct erofs_super_block {
__u8 uuid[16]; /* 128-bit uuid for volume */
__u8 volume_name[16]; /* volume name */
__le32 feature_incompat;
- __u8 reserved2[44];
+ __le16 compr_alg; /* compression algorithm specific parameters */
+ __u8 reserved2[42];
};

/*
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 67a7ec945686..f1c99dc2659f 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -70,6 +70,9 @@ struct erofs_sb_info {

/* pseudo inode to manage cached pages */
struct inode *managed_cache;
+
+ /* compression algorithm specific parameters */
+ u16 compr_alg;
#endif /* CONFIG_EROFS_FS_ZIP */
u32 blocks;
u32 meta_blkaddr;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index d5a6b9b888a5..198435e3eb2d 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -174,6 +174,9 @@ static int erofs_read_superblock(struct super_block *sb)
sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
sbi->root_nid = le16_to_cpu(dsb->root_nid);
sbi->inos = le64_to_cpu(dsb->inos);
+#ifdef CONFIG_EROFS_FS_ZIP
+ sbi->compr_alg = le16_to_cpu(dsb->compr_alg);
+#endif

sbi->build_time = le64_to_cpu(dsb->build_time);
sbi->build_time_nsec = le32_to_cpu(dsb->build_time_nsec);
--
2.25.1
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