fat: make discard a mount option

Currently shipping discard capable SSDs and arrays have rather sub-optimal
implementations of the command and can the use of it can cause massive
slowdowns.  Make issueing these commands option as it's already in btrfs
and gfs2.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[hirofumi@mail.parknet.co.jp: tweaks, and add "discard" to fat_show_options]
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

1 files changed, 15 insertions, 10 deletions

diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index a81037721a6f..81184d3b75a3 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -566,16 +566,21 @@ int fat_free_clusters(struct inode *inode, int cluster)
                         goto error;
                 }
 
-                /* 
-                 * Issue discard for the sectors we no longer care about,
-                 * batching contiguous clusters into one request
-                 */
-                if (cluster != fatent.entry + 1) {
-                        int nr_clus = fatent.entry - first_cl + 1;
-
-                        sb_issue_discard(sb, fat_clus_to_blknr(sbi, first_cl),
-                                         nr_clus * sbi->sec_per_clus);
-                        first_cl = cluster;
+                if (sbi->options.discard) {
+                        /*
+                         * Issue discard for the sectors we no longer
+                         * care about, batching contiguous clusters
+                         * into one request
+                         */
+                        if (cluster != fatent.entry + 1) {
+                                int nr_clus = fatent.entry - first_cl + 1;
+
+                                sb_issue_discard(sb,
+                                        fat_clus_to_blknr(sbi, first_cl),
+                                        nr_clus * sbi->sec_per_clus);
+
+                                first_cl = cluster;
+                        }
                 }
 
                 ops->ent_put(&fatent, FAT_ENT_FREE);