linux-kernel - [PATCH v2] f2fs: remove redundant lines in allocate_data

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Date:	Wed, 30 Jul 2014 06:52:43 +0000 (GMT)
From:	Dongho Sim <dh.sim@...sung.com>
To:	"jaegeuk@...nel.org" <jaegeuk@...nel.org>
Cc:	"linux-f2fs-devel@...ts.sourceforge.net" 
	<linux-f2fs-devel@...ts.sourceforge.net>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] f2fs: remove redundant lines in allocate_data_block

There are redundant lines in allocate_data_block.

In this function, we call refresh_sit_entry with old seg and old curseg.
After that, we call locate_dirty_segment with old curseg.

But, the new address is always allocated from old curseg and
we call locate_dirty_segment with old curseg in refresh_sit_entry.
So, we do not need to call locate_dirty_segment with old curseg again.

We've discussed like below:

Jaegeuk said:
 "When considering SSR, we need to take care of the following scenario.
  - old segno : X
  - new address : Z
  - old curseg : Y
  This means, a new block is supposed to be written to Z from X.
  And Z is newly allocated in the same path from Y.

  In that case, we should trigger locate_dirty_segment for Y, since
  it was a current_segment and can be dirty owing to SSR.
  But that was not included in the dirty list."

Changman said:
 "We already choosed old curseg(Y) and then we allocate new address(Z) from old
  curseg(Y). After that we call refresh_sit_entry(old address, new address).
  In the funcation, we call locate_dirty_segment with old seg and old curseg.
  So calling locate_dirty_segment after refresh_sit_entry again is redundant."

Jaegeuk said:
 "Right. The new address is always allocated from old_curseg."

Signed-off-by: Dongho Sim <dh.sim@...sung.com>
---
 fs/f2fs/segment.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 8a6e57d..7af4a8d 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -973,14 +973,12 @@ void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 {
 	struct sit_info *sit_i = SIT_I(sbi);
 	struct curseg_info *curseg;
-	unsigned int old_cursegno;

 	curseg = CURSEG_I(sbi, type);

 	mutex_lock(&curseg->curseg_mutex);

 	*new_blkaddr = NEXT_FREE_BLKADDR(sbi, curseg);
-	old_cursegno = curseg->segno;

 	/*
 	 * __add_sum_entry should be resided under the curseg_mutex
@@ -1001,7 +999,6 @@ void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 	 * since SSR needs latest valid block information.
 	 */
 	refresh_sit_entry(sbi, old_blkaddr, *new_blkaddr);
-	locate_dirty_segment(sbi, old_cursegno);

 	mutex_unlock(&sit_i->sentry_lock);

-- 
1.9.1