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Date: Tue, 30 Jun 2009 15:02:10 -0500
From: steve@...idescorp.com
To: hirofumi@...l.parknet.co.jp, linux-kernel@...r.kernel.org
Cc: "Steven J. Magnani" <steve@...idescorp.com>
Subject: [PATCH] FAT: optimize FSINFO writeback
Only write the FSINFO block back to disk when its contents change.
This optimization can be important when the underlying physical media
can wear out, i.e. Flash.
Signed-off-by: Steven J. Magnani <steve@...idescorp.com>
---
diff -uprN a/fs/fat/misc.c b/fs/fat/misc.c
--- a/fs/fat/misc.c 2009-06-29 11:12:40.000000000 -0500
+++ b/fs/fat/misc.c 2009-06-29 11:46:45.000000000 -0500
@@ -61,11 +61,25 @@ void fat_clusters_flush(struct super_blo
le32_to_cpu(fsinfo->signature2),
sbi->fsinfo_sector);
} else {
- if (sbi->free_clusters != -1)
- fsinfo->free_clusters = cpu_to_le32(sbi->free_clusters);
- if (sbi->prev_free != -1)
- fsinfo->next_cluster = cpu_to_le32(sbi->prev_free);
- mark_buffer_dirty(bh);
+ char write_needed = 0;
+ __le32 le_value;
+
+ if (sbi->free_clusters != -1) {
+ le_value = cpu_to_le32(sbi->free_clusters);
+ if (fsinfo->free_clusters != le_value) {
+ fsinfo->free_clusters = le_value;
+ write_needed = 1;
+ }
+ }
+ if (sbi->prev_free != -1) {
+ le_value = cpu_to_le32(sbi->prev_free);
+ if (fsinfo->next_cluster != le_value) {
+ fsinfo->next_cluster = le_value;
+ write_needed = 1;
+ }
+ }
+ if (write_needed)
+ mark_buffer_dirty(bh);
}
brelse(bh);
}
--
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