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=150， 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; >>>>>> } >>>> . >>>> >> . >> >
