Hi, Gao,
Thanks for your review !
> As for this patch, what if the inode itself is
> chunk-deduplicated, could we apply this if the inode
> only has one new chunk instead at least for now?
Do you mean inode has 3 chunks, chunk#2 and chunk#3 duplicate chunck#1?
This patch only makes the 1st chunk exactly written to blobdev aligned on
dsunit. Deduplicated chunks will not be written to blobdev.
In example above, chunk#1 is written to dsunit aligned block addr, chunk#2,#3
are not written. The next file will be written from next dsunit alignment addr.
Best Regards
Friendy Su
________________________________________
From: Gao Xiang <hsiang...@linux.alibaba.com>
Sent: Wednesday, August 20, 2025 15:44
To: Su, Friendy; linux-erofs@lists.ozlabs.org
Cc: Mo, Yuezhang; Palmer, Daniel (SGC)
Subject: Re: [PATCH v1] erofs-utils: mkfs: Implement 'dsunit' alignment on
blobdev
Hi Friendly, On 2025/8/20 15: 23, 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 Friendly,
On 2025/8/20 15:23, 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.
>
> Signed-off-by: Friendy Su <friendy...@sony.com>
> Reviewed-by: Yuezhang Mo <yuezhang...@sony.com>
> Reviewed-by: Daniel Palmer <daniel.pal...@sony.com>
Sigh, thanks for the patch! Actually the blob chunk implementation
(this file) is now an implementation debt since:
1) In principle, chunks (and deduplicated pclusters) should
across blobs (considering the main device is also a blob);
2) Each blob should have its own space allocation context
which is independent to the in-memory chunk records...
My mid-term plan tends to use the current metabox way
(i.e. use buffer management for all extra blobs too..)
> ---
> lib/blobchunk.c | 15 +++++++++++++++
> 1 file changed, 15 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) {
> + 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);
> + }
But since you have use case on the current chunk
approach, so...
As for this patch, what if the inode itself is
chunk-deduplicated, could we apply this if the inode
only has one new chunk instead at least for now?
Thanks,
Gao Xiang
