+ if (cfg.c_chunkbits && dsunit && 1u << (cfg.c_chunkbits -
g_sbi.blkszbits) < dsunit) {
+ erofs_warn("chunksize %u bytes is smaller than dsunit %u
blocks, ignore dsunit !",
+ 1u << cfg.c_chunkbits, dsunit);
+ dsunit = 0;
+ }
'ignore dsunit' means set it to default, default dsunit is 0. Is this correct?
Then sbi->bmgr->dsunit will be set to 'dsunit'.
________________________________________
From: Su, Friendy <friendy...@sony.com>
Sent: Friday, August 22, 2025 17:05
To: Gao Xiang; linux-erofs@lists.ozlabs.org
Cc: Mo, Yuezhang; Palmer, Daniel (SGC)
Subject: Re: [PATCH v2] erofs-utils: mkfs: Implement 'dsunit' alignment on
blobdev
Hi, Gao,
> It should be
> if (sbi->bmgr->dsunit >= 1u << (cfg.c_chunkbits - g_sbi.blkszbits)) {
> }
In main.c, dsunit is set to 0 if warns.
+ if (cfg.c_chunkbits && dsunit && 1u << (cfg.c_chunkbits -
g_sbi.blkszbits) < dsunit) {
+ erofs_warn("chunksize %u bytes is smaller than dsunit %u
blocks, ignore dsunit !",
+ 1u << cfg.c_chunkbits, dsunit);
+ dsunit = 0;
+ }
so here sbi->bmgr->dsunit is 0.
________________________________________
From: Gao Xiang <hsiang...@linux.alibaba.com>
Sent: Friday, August 22, 2025 16:55
To: Su, Friendy; linux-erofs@lists.ozlabs.org
Cc: Mo, Yuezhang; Palmer, Daniel (SGC)
Subject: Re: [PATCH v2] erofs-utils: mkfs: Implement 'dsunit' alignment on
blobdev
Hi Friendy, On 2025/8/22 16: 42, Friendy Su wrote: > Set proper 'dsunit' to let
file body align on huge page on blobdev, > > where 'dsunit' * 'blocksize' =
huge page size (2M). > > When do mmap() a file mounted with dax=always,
Hi Friendy,
On 2025/8/22 16:42, Friendy Su wrote:
> Set proper 'dsunit' to let file body align on huge page on blobdev,
>
> where 'dsunit' * 'blocksize' = huge page size (2M).
>
> When do mmap() a file mounted with dax=always, aligning on huge page
> makes kernel map huge page(2M) per page fault exception, compared with
> mapping normal page(4K) per page fault.
>
> This greatly improves mmap() performance by reducing times of page
> fault being triggered.
>
> Considering deduplication, 'chunksize' should not be smaller than
> 'dsunit', then after dedupliation, still align on dsunit.
>
> Signed-off-by: Friendy Su <friendy...@sony.com>
> Reviewed-by: Yuezhang Mo <yuezhang...@sony.com>
> Reviewed-by: Daniel Palmer <daniel.pal...@sony.com>
> ---
> lib/blobchunk.c | 15 +++++++++++++++
> man/mkfs.erofs.1 | 15 +++++++++++++++
> mkfs/main.c | 13 +++++++++++++
> 3 files changed, 43 insertions(+)
>
> diff --git a/lib/blobchunk.c b/lib/blobchunk.c
> index bbc69cf..e47afb5 100644
> --- a/lib/blobchunk.c
> +++ b/lib/blobchunk.c
> @@ -309,6 +309,21 @@ int erofs_blob_write_chunked_file(struct erofs_inode
> *inode, int fd,
> minextblks = BLK_ROUND_UP(sbi, inode->i_size);
> interval_start = 0;
>
> + /* Align file on 'dsunit' */
> + if (sbi->bmgr->dsunit > 1) {
It should be
if (sbi->bmgr->dsunit >= 1u << (cfg.c_chunkbits - g_sbi.blkszbits)) {
}
?
> + off_t off = lseek(blobfile, 0, SEEK_CUR);
> +
> + erofs_dbg("Try to round up 0x%llx to align on %d blocks
> (dsunit)",
> + off, sbi->bmgr->dsunit);
> + off = roundup(off, sbi->bmgr->dsunit * erofs_blksiz(sbi));
> + if (lseek(blobfile, off, SEEK_SET) != off) {
> + ret = -errno;
> + erofs_err("lseek to blobdev 0x%llx error", off);
> + goto err;
> + }
> + erofs_dbg("Aligned on 0x%llx", off);
Could we combine these two debugging messages into one?
> + }
> +
> for (pos = 0; pos < inode->i_size; pos += len) {
> #ifdef SEEK_DATA
> off_t offset = lseek(fd, pos + startoff, SEEK_DATA);
> diff --git a/man/mkfs.erofs.1 b/man/mkfs.erofs.1
> index 63f7a2f..9075522 100644
> --- a/man/mkfs.erofs.1
> +++ b/man/mkfs.erofs.1
> @@ -168,6 +168,21 @@ the output filesystem, with no leading /.
> .TP
> .BI "\-\-dsunit=" #
> Align all data block addresses to multiples of #.
> +
> +If \fBdsunit\fR and \fBchunksize\fR are both set, \fBdsunit\fR will be
> ignored
> +if it is bigger than \fBchunksize\fR.
> +
> +This is for keeping alignment after deduplication.
> +If \fBdsunit\fR is bigger, it contains several chunks,
> +
> +E.g. \fBblock-size\fR=4096, \fBdsunit\fR=512 (2M), \fBchunksize\fR=4096
> +
> +Once 1 chunk is deduplicated, the chunks thereafter will not be aligned any
> +longer. In order to achieve the best performance, recommend to set
> \fBdsunit\fR
> +same as \fBchunksize\fR.
> +
> +E.g. \fBblock-size\fR=4096, \fBdsunit\fR=512 (2M),
> \fBchunksize\fR=$((4096*512))
> +
> .TP
> .BI "\-\-exclude-path=" path
> Ignore file that matches the exact literal path.
> diff --git a/mkfs/main.c b/mkfs/main.c
> index 30804d1..fcb2b89 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -1098,6 +1098,19 @@ static int mkfs_parse_options_cfg(int argc, char
> *argv[])
> return -EINVAL;
> }
>
> + /*
> + * once align data on dsunit, in order to keep alignment after
> deduplication
> + * chunksize should be equal to or bigger than dsunit.
> + * if chunksize is smaller than dsunit, e.g. chunksize=4k, dsunit=2M,
> + * once a chunk is deduplicated, all data thereafter will be unaligned.
> + * so ignore dsunit under such case.
> + */
> + if (cfg.c_chunkbits && dsunit && 1u << (cfg.c_chunkbits -
> g_sbi.blkszbits) < dsunit) {
> + erofs_warn("chunksize %u bytes is smaller than dsunit %u
> blocks, ignore dsunit !",
> + 1u << cfg.c_chunkbits, dsunit);
One tab is not 8 spaces here? it seems indent misalignment.
Thanks,
Gao Xiang
