Re: [PATCH] erofs-utils: mkfs: skip the redundant write for ztailpacking block

[Yifan Zhao]

On 4/18/24 9:09 AM, Noboru Asai wrote:
In this patch, the value of blkaddr in z_erofs_lcluster_index
corresponding to the ztailpacking block in the extent list
is invalid value. It looks that the linux kernel doesn't refer to this
value, but what value is correct?
0 or -1 (EROFS_NULL_ADDR) or don't care?

For the read side, AFAIK the kernel (and also the user lib of 
erofs-utils) will turn to the meta for inlined data

for read offset beyond the last data block if ztailpacking is enabled, 
see `erofs_map_blocks_flatmode`.

So I believe the blkaddr recorded in z_erofs_lcluster_index is 
irrelevant and we don't need to care about it.


For the mkfs side I think things could be polished according to Gao's 
review opinion.


Thanks,

Yifan Zhao


2024年4月17日(水) 23:43 Yifan Zhao <zhaoyi...@sjtu.edu.cn>:
z_erofs_merge_segment() doesn't consider the ztailpacking block in the
extent list and unnecessarily writes it back to the disk. This patch
fixes this issue by introducing a new `inlined` field in the struct
`z_erofs_inmem_extent`.

Signed-off-by: Yifan Zhao <zhaoyi...@sjtu.edu.cn>
---
  include/erofs/dedupe.h | 2 +-
  lib/compress.c         | 8 ++++++++
  lib/dedupe.c           | 1 +
  3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/erofs/dedupe.h b/include/erofs/dedupe.h
index 153bd4c..4cbfb2c 100644
--- a/include/erofs/dedupe.h
+++ b/include/erofs/dedupe.h
@@ -16,7 +16,7 @@ struct z_erofs_inmem_extent {
         erofs_blk_t blkaddr;
         unsigned int compressedblks;
         unsigned int length;
-       bool raw, partial;
+       bool raw, partial, inlined;
  };

  struct z_erofs_dedupe_ctx {
diff --git a/lib/compress.c b/lib/compress.c
index 74c5707..41628e7 100644
--- a/lib/compress.c
+++ b/lib/compress.c
@@ -572,6 +572,7 @@ nocompression:
                  */
                 e->compressedblks = 1;
                 e->raw = true;
+               e->inlined = false;
         } else if (may_packing && len == e->length &&
                    compressedsize < ctx->pclustersize &&
                    (!inode->fragment_size || ictx->fix_dedupedfrag)) {
@@ -582,6 +583,7 @@ frag_packing:
                         return ret;
                 e->compressedblks = 0; /* indicate a fragment */
                 e->raw = false;
+               e->inlined = false;
                 ictx->fragemitted = true;
         /* tailpcluster should be less than 1 block */
         } else if (may_inline && len == e->length && compressedsize < blksz) {
@@ -600,6 +602,7 @@ frag_packing:
                         return ret;
                 e->compressedblks = 1;
                 e->raw = false;
+               e->inlined = true;
         } else {
                 unsigned int tailused, padding;

@@ -652,6 +655,7 @@ frag_packing:
                                 return ret;
                 }
                 e->raw = false;
+               e->inlined = false;
                 may_inline = false;
                 may_packing = false;
         }
@@ -1151,6 +1155,9 @@ int z_erofs_merge_segment(struct z_erofs_compress_ictx 
*ictx,
                 ei->e.blkaddr = sctx->blkaddr;
                 sctx->blkaddr += ei->e.compressedblks;

+               if (ei->e.inlined)
+                       continue;
+
                 ret2 = blk_write(sbi, sctx->membuf + blkoff * 
erofs_blksiz(sbi),
                                  ei->e.blkaddr, ei->e.compressedblks);
                 blkoff += ei->e.compressedblks;
@@ -1374,6 +1381,7 @@ int erofs_write_compressed_file(struct erofs_inode 
*inode, int fd, u64 fpos)
                         .compressedblks = 0,
                         .raw = false,
                         .partial = false,
+                       .inlined = false,
                         .blkaddr = sctx.blkaddr,
                 };
                 init_list_head(&ei->list);
diff --git a/lib/dedupe.c b/lib/dedupe.c
index 19a1c8d..aaaccb5 100644
--- a/lib/dedupe.c
+++ b/lib/dedupe.c
@@ -138,6 +138,7 @@ int z_erofs_dedupe_match(struct z_erofs_dedupe_ctx *ctx)
                 ctx->e.partial = e->partial ||
                         (window_size + extra < e->original_length);
                 ctx->e.raw = e->raw;
+               ctx->e.inlined = false;
                 ctx->e.blkaddr = e->compressed_blkaddr;
                 ctx->e.compressedblks = e->compressed_blks;
                 return 0;
--
2.44.0