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authorFilipe Manana <fdmanana@suse.com>2018-02-06 20:40:40 +0000
committerDavid Sterba <dsterba@suse.com>2018-03-26 15:09:41 +0200
commitffa7c4296e93b25fc302c209ae488e57aad4c973 (patch)
tree2b15939312b1731ba975bb5cf7bc23a2d021d46d /fs/btrfs/send.c
parent213e8c5520ed1ecc5401a3a0f716b51a7318bda9 (diff)
Btrfs: send, do not issue unnecessary truncate operations
When send finishes processing an inode representing a regular file, it always issues a truncate operation for that file, even if its size did not change or the last write sets the file size correctly. In the most common cases, the issued write operations set the file to correct size (either full or incremental sends) or the file size did not change (for incremental sends), so the only case where a truncate operation is needed is when a file size becomes smaller in the send snapshot when compared to the parent snapshot. By not issuing unnecessary truncate operations we reduce the stream size and save time in the receiver. Currently truncating a file to the same size triggers writeback of its last page (if it's dirty) and waits for it to complete (only if the file size is not aligned with the filesystem's sector size). This is being fixed by another patch and is independent of this change (that patch's title is "Btrfs: skip writeback of last page when truncating file to same size"). The following script was used to measure time spent by a receiver without this change applied, with this change applied, and without this change and with the truncate fix applied (the fix to not make it start and wait for writeback to complete). $ cat test_send.sh #!/bin/bash SRC_DEV=/dev/sdc DST_DEV=/dev/sdd SRC_MNT=/mnt/sdc DST_MNT=/mnt/sdd mkfs.btrfs -f $SRC_DEV >/dev/null mkfs.btrfs -f $DST_DEV >/dev/null mount $SRC_DEV $SRC_MNT mount $DST_DEV $DST_MNT echo "Creating source filesystem" for ((t = 0; t < 10; t++)); do ( for ((i = 1; i <= 20000; i++)); do xfs_io -f -c "pwrite -S 0xab 0 5000" \ $SRC_MNT/file_$i > /dev/null done ) & worker_pids[$t]=$! done wait ${worker_pids[@]} echo "Creating and sending snapshot" btrfs subvolume snapshot -r $SRC_MNT $SRC_MNT/snap1 >/dev/null /usr/bin/time -f "send took %e seconds" \ btrfs send -f $SRC_MNT/send_file $SRC_MNT/snap1 /usr/bin/time -f "receive took %e seconds" \ btrfs receive -f $SRC_MNT/send_file $DST_MNT umount $SRC_MNT umount $DST_MNT The results, which are averages for 5 runs for each case, were the following: * Without this change average receive time was 26.49 seconds standard deviation of 2.53 seconds * Without this change and with the truncate fix average receive time was 12.51 seconds standard deviation of 0.32 seconds * With this change and without the truncate fix average receive time was 10.02 seconds standard deviation of 1.11 seconds Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/send.c')
-rw-r--r--fs/btrfs/send.c26
1 files changed, 21 insertions, 5 deletions
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 085542832b9a..6615d849f0f0 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -112,6 +112,7 @@ struct send_ctx {
u64 cur_inode_mode;
u64 cur_inode_rdev;
u64 cur_inode_last_extent;
+ u64 cur_inode_next_write_offset;
u64 send_progress;
@@ -5030,6 +5031,7 @@ static int send_hole(struct send_ctx *sctx, u64 end)
break;
offset += len;
}
+ sctx->cur_inode_next_write_offset = offset;
tlv_put_failure:
fs_path_free(p);
return ret;
@@ -5265,6 +5267,7 @@ static int send_write_or_clone(struct send_ctx *sctx,
} else {
ret = send_extent_data(sctx, offset, len);
}
+ sctx->cur_inode_next_write_offset = offset + len;
out:
return ret;
}
@@ -5789,6 +5792,7 @@ static int finish_inode_if_needed(struct send_ctx *sctx, int at_end)
u64 right_gid;
int need_chmod = 0;
int need_chown = 0;
+ int need_truncate = 1;
int pending_move = 0;
int refs_processed = 0;
@@ -5826,9 +5830,13 @@ static int finish_inode_if_needed(struct send_ctx *sctx, int at_end)
need_chown = 1;
if (!S_ISLNK(sctx->cur_inode_mode))
need_chmod = 1;
+ if (sctx->cur_inode_next_write_offset == sctx->cur_inode_size)
+ need_truncate = 0;
} else {
+ u64 old_size;
+
ret = get_inode_info(sctx->parent_root, sctx->cur_ino,
- NULL, NULL, &right_mode, &right_uid,
+ &old_size, NULL, &right_mode, &right_uid,
&right_gid, NULL);
if (ret < 0)
goto out;
@@ -5837,6 +5845,10 @@ static int finish_inode_if_needed(struct send_ctx *sctx, int at_end)
need_chown = 1;
if (!S_ISLNK(sctx->cur_inode_mode) && left_mode != right_mode)
need_chmod = 1;
+ if ((old_size == sctx->cur_inode_size) ||
+ (sctx->cur_inode_size > old_size &&
+ sctx->cur_inode_next_write_offset == sctx->cur_inode_size))
+ need_truncate = 0;
}
if (S_ISREG(sctx->cur_inode_mode)) {
@@ -5855,10 +5867,13 @@ static int finish_inode_if_needed(struct send_ctx *sctx, int at_end)
goto out;
}
}
- ret = send_truncate(sctx, sctx->cur_ino, sctx->cur_inode_gen,
- sctx->cur_inode_size);
- if (ret < 0)
- goto out;
+ if (need_truncate) {
+ ret = send_truncate(sctx, sctx->cur_ino,
+ sctx->cur_inode_gen,
+ sctx->cur_inode_size);
+ if (ret < 0)
+ goto out;
+ }
}
if (need_chown) {
@@ -5912,6 +5927,7 @@ static int changed_inode(struct send_ctx *sctx,
sctx->cur_ino = key->objectid;
sctx->cur_inode_new_gen = 0;
sctx->cur_inode_last_extent = (u64)-1;
+ sctx->cur_inode_next_write_offset = 0;
/*
* Set send_progress to current inode. This will tell all get_cur_xxx