linux-kernel - [f2fs-dev] [PATCH] f2fs: change the method of calculating the number summary blocks

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Date:	Mon, 28 Oct 2013 08:54:28 +0000 (GMT)
From:	Fan Li <fanofcode.li@...sung.com>
To:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-f2fs-devel@...ts.sourceforge.net" 
	<linux-f2fs-devel@...ts.sourceforge.net>
Subject: [f2fs-dev] [PATCH] f2fs: change the method of calculating the number
 summary blocks

"There is a HTML error in the previous email, so I send this one.If you already received this before, please ignore it.Sorry for the inconvenience"

This patch change the method of calculating the number of summary blocks in function  npages_for_summary_flush.
npages_for_summary_flush uses (SUMMARY_SIZE + 1) as the size of a f2fs_summary while the actual size is just SUMMARY_SIZE.
As a result, occasionally the return value of npages_for_summary_flush will be bigger than the actual number by one, and the checkpoint won't be written contiguously  into disk.
Besides, struct f2fs_summary can't be split to two pages, so it could take more space than the sum of its size, the current version seems not to take it into account.

Signed-off-by: Fan Li <fanofcode.li@...sung.com>
---
 fs/f2fs/segment.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index 487af61..ba2930f 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -279,9 +279,8 @@ static void __add_sum_entry(struct f2fs_sb_info *sbi, int type,
  */
 int npages_for_summary_flush(struct f2fs_sb_info *sbi)  {
-	int total_size_bytes = 0;
 	int valid_sum_count = 0;
-	int i, sum_space;
+	int i, sum_in_page;
 
 	for (i = CURSEG_HOT_DATA; i <= CURSEG_COLD_DATA; i++) {
 		if (sbi->ckpt->alloc_type[i] == SSR)
@@ -290,13 +289,12 @@ int npages_for_summary_flush(struct f2fs_sb_info *sbi)
 			valid_sum_count += curseg_blkoff(sbi, i);
 	}
 
-	total_size_bytes = valid_sum_count * (SUMMARY_SIZE + 1)
-			+ sizeof(struct nat_journal) + 2
-			+ sizeof(struct sit_journal) + 2;
-	sum_space = PAGE_CACHE_SIZE - SUM_FOOTER_SIZE;
-	if (total_size_bytes < sum_space)
+	sum_in_page = (PAGE_CACHE_SIZE - 2*SUM_JOURNAL_SIZE - SUM_FOOTER_SIZE)/
+			SUMMARY_SIZE;
+	if (valid_sum_count <= sum_in_page)
 		return 1;
-	else if (total_size_bytes < 2 * sum_space)
+	else if (valid_sum_count-sum_in_page <=
+			(PAGE_CACHE_SIZE-SUM_FOOTER_SIZE)/SUMMARY_SIZE)
 		return 2;
 	return 3;
 }
--
1.7.9.5