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
