Re: [PATCH v3] f2fs: add cur_reserved_blocks to support soft block reservation
From: Yunlong Song
Date: Wed Oct 25 2017 - 23:32:00 EST
Agree
On 2017/10/26 11:26, Chao Yu wrote:
On 2017/10/26 11:07, Yunlong Song wrote:
Yes, I agree with the soft semantic you introduce, it is too slow to
increase cur_reserved_blocks only in
dec_valid_block(,node)_count, e.g. if users want to set
cur_reserved_blocks to 10G.
Yup,
Then how about fix the initialization of cur_reserved_blocks in
fs/f2fs/super.c as following:
sbi->current_reserved_blocks = 0
change to
sbi->current_reserved_blocks = min(sbi->reserved_blocks,
sbi->user_block_count - valid_user_blocks(sbi));
It will be necessary only if reserved_blocks is initialized with a non-zero value,
but now it has value of zero, so it's redundant...
What about adding this check if we initialize reserved_blocks with a non-zero default
value or value which may be configured with mount_option?
Thanks,
On 2017/10/25 23:46, Chao Yu wrote:
On 2017/10/25 22:06, Yunlong Song wrote:
Hi, Chao,
Please see my comments below.
On 2017/10/25 20:26, Chao Yu wrote:
On 2017/10/25 18:02, Yunlong Song wrote:
ping...
I've replied in this thread, check your email list please, or you can check the
comments in below link:
https://patchwork.kernel.org/patch/9909407/
Anyway, see comments below.
On 2017/8/18 23:09, Yunlong Song wrote:
This patch adds cur_reserved_blocks to extend reserved_blocks sysfs
interface to be soft threshold, which allows user configure it exceeding
current available user space. To ensure there is enough space for
supporting system's activation, this patch does not set the reserved space
to the configured reserved_blocks value at once, instead, it safely
increase cur_reserved_blocks in dev_valid_block(,node)_count to only take
up the blocks which are just obsoleted.
Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-fs-f2fs | 3 ++-
fs/f2fs/f2fs.h | 13 +++++++++++--
fs/f2fs/super.c | 3 ++-
fs/f2fs/sysfs.c | 15 +++++++++++++--
4 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index 11b7f4e..ba282ca 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -138,7 +138,8 @@ What: /sys/fs/f2fs/<disk>/reserved_blocks
Date: June 2017
Contact: "Chao Yu" <yuchao0@xxxxxxxxxx>
Description:
- Controls current reserved blocks in system.
+ Controls current reserved blocks in system, the threshold
+ is soft, it could exceed current available user space.
What: /sys/fs/f2fs/<disk>/gc_urgent
Date: August 2017
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 2f20b6b..84ccbdc 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1041,6 +1041,7 @@ struct f2fs_sb_info {
block_t discard_blks; /* discard command candidats */
block_t last_valid_block_count; /* for recovery */
block_t reserved_blocks; /* configurable reserved blocks */
+ block_t cur_reserved_blocks; /* current reserved blocks */
u32 s_next_generation; /* for NFS support */
@@ -1515,7 +1516,8 @@ static inline int inc_valid_block_count(struct f2fs_sb_info *sbi,
spin_lock(&sbi->stat_lock);
sbi->total_valid_block_count += (block_t)(*count);
- avail_user_block_count = sbi->user_block_count - sbi->reserved_blocks;
+ avail_user_block_count = sbi->user_block_count -
+ sbi->cur_reserved_blocks;
if (unlikely(sbi->total_valid_block_count > avail_user_block_count)) {
diff = sbi->total_valid_block_count - avail_user_block_count;
*count -= diff;
@@ -1549,6 +1551,10 @@ static inline void dec_valid_block_count(struct f2fs_sb_info *sbi,
f2fs_bug_on(sbi, sbi->total_valid_block_count < (block_t) count);
f2fs_bug_on(sbi, inode->i_blocks < sectors);
sbi->total_valid_block_count -= (block_t)count;
+ if (sbi->reserved_blocks &&
+ sbi->reserved_blocks != sbi->cur_reserved_blocks)
It's redundent check here...
I think in most cases, cur_reserved_blocks is equal to reserved_blocks, so we do not need to calculate min any more, otherwise,
if reserved_blocks is not 0, it will calculate min and set current_reserved_blocks each time.
OK, IMO, in some condition, we can save dirtying cache line to decrease cache
line missing with that check.
+ sbi->cur_reserved_blocks = min(sbi->reserved_blocks,
+ sbi->cur_reserved_blocks + count);
spin_unlock(&sbi->stat_lock);
f2fs_i_blocks_write(inode, count, false, true);
}
@@ -1695,7 +1701,7 @@ static inline int inc_valid_node_count(struct f2fs_sb_info *sbi,
spin_lock(&sbi->stat_lock);
valid_block_count = sbi->total_valid_block_count + 1;
- if (unlikely(valid_block_count + sbi->reserved_blocks >
+ if (unlikely(valid_block_count + sbi->cur_reserved_blocks >
sbi->user_block_count)) {
spin_unlock(&sbi->stat_lock);
goto enospc;
@@ -1738,6 +1744,9 @@ static inline void dec_valid_node_count(struct f2fs_sb_info *sbi,
sbi->total_valid_node_count--;
sbi->total_valid_block_count--;
+ if (sbi->reserved_blocks &&
+ sbi->reserved_blocks != sbi->cur_reserved_blocks)
Checking low boundary is more safe here.
I think cur_reserved_blocks can never be larger than reserved_blocks in any case. so min(reserved_blocks,
cur_reserved_blocks +1) is same to cur_reserved_blocks++ when reserved_blocks != cur_reserved_blocks
(which means reserved_blocks > cur_reserved_block )
Ditto.
+ sbi->cur_reserved_blocks++;
spin_unlock(&sbi->stat_lock);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 4c1bdcb..16a805f 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -957,7 +957,7 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
buf->f_blocks = total_count - start_count;
buf->f_bfree = user_block_count - valid_user_blocks(sbi) + ovp_count;
buf->f_bavail = user_block_count - valid_user_blocks(sbi) -
- sbi->reserved_blocks;
+ sbi->cur_reserved_blocks;
avail_node_count = sbi->total_node_count - F2FS_RESERVED_NODE_NUM;
@@ -2411,6 +2411,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
le64_to_cpu(sbi->ckpt->valid_block_count);
sbi->last_valid_block_count = sbi->total_valid_block_count;
sbi->reserved_blocks = 0;
+ sbi->cur_reserved_blocks = 0;
for (i = 0; i < NR_INODE_TYPE; i++) {
INIT_LIST_HEAD(&sbi->inode_list[i]);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index a1be5ac..75c37bb 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -104,12 +104,22 @@ static ssize_t features_show(struct f2fs_attr *a,
return len;
}
+static ssize_t f2fs_reserved_blocks_show(struct f2fs_attr *a,
+ struct f2fs_sb_info *sbi, char *buf)
+{
+ return snprintf(buf, PAGE_SIZE, "expected: %u\ncurrent: %u\n",
+ sbi->reserved_blocks, sbi->cur_reserved_blocks);
+}
+
static ssize_t f2fs_sbi_show(struct f2fs_attr *a,
struct f2fs_sb_info *sbi, char *buf)
{
unsigned char *ptr = NULL;
unsigned int *ui;
+ if (a->struct_type == RESERVED_BLOCKS)
+ return f2fs_reserved_blocks_show(a, sbi, buf);
+
ptr = __struct_ptr(sbi, a->struct_type);
if (!ptr)
return -EINVAL;
@@ -143,12 +153,13 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
#endif
if (a->struct_type == RESERVED_BLOCKS) {
spin_lock(&sbi->stat_lock);
- if ((unsigned long)sbi->total_valid_block_count + t >
- (unsigned long)sbi->user_block_count) {
+ if (t > (unsigned long)sbi->user_block_count) {
spin_unlock(&sbi->stat_lock);
return -EINVAL;
}
*ui = t;
+ if (t < (unsigned long)sbi->cur_reserved_blocks)
+ sbi->cur_reserved_blocks = t;
No, for 't < cur_reserved_blocks' case, cur_reserved_blocks will out of update
even if there is enough free space. You know, for soft block resevation, we need
to reserve blocks as many as possible, making free space being zero suddenly is
possible.
I do not understand why it is not safe to decrease cur_reserved_blocks, for example,
if current cur_reserved_blocks is 100, now decrease it to 80, is there any problem?
If 80 will make free space zero, how does 100 exist?
And I do not think it is safe as following:
*ui = t;
+ sbi->current_reserved_blocks = min(sbi->reserved_blocks,
+ sbi->user_block_count - valid_user_blocks(sbi));
If user_block_count = 200, valid_user_blocks=150ï reserved_blocks = 100,
then current_reserved_block = min(100,200-50) = 50, in this case, free space
is suddenly becoming zero.
Free space becomes zero suddenly is safe, as I said before, I don't expect this
feature can be used in android, instead, it may be used in distributed storage
scenario, in where, once we configure soft_reserved_block making one server out
of free space, it's not critical issue to this system since we can move current
copy to another server which has enough free space.
Secondly, as an global configuration, it's due to usage of administrator with
it, if there is critical application which is sensitive with free space,
administrator should make sure our reservation should not overload consuming free
space, which means soft reservation is not suitable.
To avoid this, I change the code to:
+ if (t < (unsigned long)sbi->cur_reserved_blocks)
+ sbi->cur_reserved_blocks = t;
I think it is only safe to decrease the value of cur_reserved_blocks, and leave increase operation to
dec_valid_block(,node)_count, it is safe to increase cur_reserved_blocks there.
For initialization of reserved_blocks, cur_reserved_blocks will always be zero
due to this check, and will be updated to close to reserved_blocks after block
allocation and deallocation of user, IMO, it's not looks reasonable to user.
Anyway, it's due to how you define semantics of soft reservation, so what is your
understanding of it?
Thanks,
Thanks,
spin_unlock(&sbi->stat_lock);
return count;
}
.
.
.
--
Thanks,
Yunlong Song