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Message-ID: <8169edfd-de1d-e2de-4805-c7e3ce8d7502@huawei.com>
Date: Sat, 27 Mar 2021 17:34:33 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Gao Xiang <hsiangkao@....com>, <linux-erofs@...ts.ozlabs.org>,
Chao Yu <chao@...nel.org>
CC: LKML <linux-kernel@...r.kernel.org>,
Huang Jianan <huangjianan@...o.com>,
Guo Weichao <guoweichao@...o.com>,
Gao Xiang <hsiangkao@...hat.com>
Subject: Re: [PATCH 2/4] erofs: support adjust lz4 history window size
On 2021/3/27 11:49, Gao Xiang wrote:
> From: Huang Jianan <huangjianan@...o.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.
>
> 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.
>
> Signed-off-by: Huang Jianan <huangjianan@...o.com>
> Signed-off-by: Guo Weichao <guoweichao@...o.com>
> [ Gao Xiang: introduce struct erofs_sb_lz4_info for configurations. ]
> Signed-off-by: Gao Xiang <hsiangkao@...hat.com>
> ---
> fs/erofs/decompressor.c | 21 +++++++++++++++++----
> fs/erofs/erofs_fs.h | 3 ++-
> fs/erofs/internal.h | 19 +++++++++++++++++++
> fs/erofs/super.c | 4 +++-
> 4 files changed, 41 insertions(+), 6 deletions(-)
>
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 80e8871aef71..93411e9df9b6 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -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) {
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index 9ad1615f4474..b27d0e4e4ab5 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 lz4_max_distance;
It missed to add comments, otherwise it looks good to me.
Reviewed-by: Chao Yu <yuchao0@...wei.com>
Thanks,
> + __u8 reserved2[42];
> };
>
> /*
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index d29fc0c56032..1de60992c3dd 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -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;
> @@ -432,6 +440,8 @@ 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) {}
> @@ -439,6 +449,15 @@ 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 */
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 991b99eaf22a..3212e4f73f85 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -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);
>
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