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authorNikolay Borisov <nborisov@suse.com>2019-09-27 13:23:16 +0300
committerDavid Sterba <dsterba@suse.com>2019-11-18 14:46:59 +0300
commitd79b7c26b12279038b8b84bfcbe7bb3e53382b3f (patch)
tree4140bd7e654c040161b9cf0c4040639dddedbbaa /fs
parent0cf252131361cdeebb7dfc88dd8ec825fff0956a (diff)
downloadlinux-d79b7c26b12279038b8b84bfcbe7bb3e53382b3f.tar.xz
btrfs: Speed up btrfs_file_llseek
Modifying the file position is done on a per-file basis. This renders holding the inode lock for writing useless and makes the performance of concurrent llseek's abysmal. Fix this by holding the inode for read. This provides protection against concurrent truncates and find_desired_extent already includes proper extent locking for the range which ensures proper locking against concurrent writes. SEEK_CUR and SEEK_END can be done lockessly. The former is synchronized by file::f_lock spinlock. SEEK_END is not synchronized but atomic, but that's OK since there is not guarantee that SEEK_END will always be at the end of the file in the face of tail modifications. This change brings ~82% performance improvement when doing a lot of parallel fseeks. The workload essentially does: for (d=0; d<num_seek_read; d++) { /* offset %= 16777216; */ fseek (f, 256 * d % 16777216, SEEK_SET); fread (buffer, 64, 1, f); } Without patch: num workprocesses = 16 num fseek/fread = 8000000 step = 256 fork 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 real 0m41.412s user 0m28.777s sys 2m16.510s With patch: num workprocesses = 16 num fseek/fread = 8000000 step = 256 fork 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 real 0m11.479s user 0m27.629s sys 0m21.040s Signed-off-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/file.c26
1 files changed, 10 insertions, 16 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 91c98a6d1408..35cfc738f6b7 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3356,13 +3356,14 @@ static int find_desired_extent(struct inode *inode, loff_t *offset, int whence)
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct extent_map *em = NULL;
struct extent_state *cached_state = NULL;
+ loff_t i_size = inode->i_size;
u64 lockstart;
u64 lockend;
u64 start;
u64 len;
int ret = 0;
- if (inode->i_size == 0)
+ if (i_size == 0 || *offset >= i_size)
return -ENXIO;
/*
@@ -3372,8 +3373,7 @@ static int find_desired_extent(struct inode *inode, loff_t *offset, int whence)
start = max_t(loff_t, 0, *offset);
lockstart = round_down(start, fs_info->sectorsize);
- lockend = round_up(i_size_read(inode),
- fs_info->sectorsize);
+ lockend = round_up(i_size, fs_info->sectorsize);
if (lockend <= lockstart)
lockend = lockstart + fs_info->sectorsize;
lockend--;
@@ -3382,7 +3382,7 @@ static int find_desired_extent(struct inode *inode, loff_t *offset, int whence)
lock_extent_bits(&BTRFS_I(inode)->io_tree, lockstart, lockend,
&cached_state);
- while (start < inode->i_size) {
+ while (start < i_size) {
em = btrfs_get_extent_fiemap(BTRFS_I(inode), start, len);
if (IS_ERR(em)) {
ret = PTR_ERR(em);
@@ -3406,10 +3406,10 @@ static int find_desired_extent(struct inode *inode, loff_t *offset, int whence)
}
free_extent_map(em);
if (!ret) {
- if (whence == SEEK_DATA && start >= inode->i_size)
+ if (whence == SEEK_DATA && start >= i_size)
ret = -ENXIO;
else
- *offset = min_t(loff_t, start, inode->i_size);
+ *offset = min_t(loff_t, start, i_size);
}
unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
&cached_state);
@@ -3421,7 +3421,6 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
struct inode *inode = file->f_mapping->host;
int ret;
- inode_lock(inode);
switch (whence) {
case SEEK_END:
case SEEK_CUR:
@@ -3429,21 +3428,16 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
goto out;
case SEEK_DATA:
case SEEK_HOLE:
- if (offset >= i_size_read(inode)) {
- inode_unlock(inode);
- return -ENXIO;
- }
-
+ inode_lock_shared(inode);
ret = find_desired_extent(inode, &offset, whence);
- if (ret) {
- inode_unlock(inode);
+ inode_unlock_shared(inode);
+
+ if (ret)
return ret;
- }
}
offset = vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
out:
- inode_unlock(inode);
return offset;
}