Date:   Sat, 18 Mar 2017 11:16:26 +0300
From:   Alexey Lyashkov <alexey.lyashkov@...il.com>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Artem Blagodarenko <artem.blagodarenko@...il.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        Yang Sheng <yang.sheng@...el.com>,
        Zhen Liang <liang.zhen@...el.com>,
        Artem Blagodarenko <artem.blagodarenko@...gate.com>
Subject: Re: [PATCH] Add largedir feature

Andreas,

it not about a feature flag. It’s about a situation in whole.
Yes, we may increase a directory size, but it open a number a large problems.
1) readdir. It tries to read all entries in memory before send to the user. currently it may eats 20*10^6 * 256 so several gigs, so increasing it size may produce a problems for a system.
2) inode allocation. Current code tries to allocate an inode as near as possible to the directory inode, but one GD may hold 32k entries only, so increase a directory size will use up 1k GD for now and more than it, after it. It increase a seek time with file allocation. It was i mean when say - «dramatically decrease a file creation rate».
3) current limit with 4G inodes - currently 32-128 directories may eats a full inode number space. From it perspective large dir don’t need to be used.

Other improvements you point already. 

> 17 марта 2017 г., в 23:51, Andreas Dilger <adilger@...ger.ca> написал(а):
> 
> On Mar 17, 2017, at 12:15 AM, Alexey Lyashkov <alexey.lyashkov@...il.com> wrote:
>> 
>> Andreas,
>> 
>> I not strongly against it patch, but my testing say - 3 level h-tree need a more than 20mil files in directory, and creation rate was dropped dramatically,
>> a specially without parallel dir operations, Did we need do some other research changes with landing it patch as disk format will changed anyway by incompatible way ?
> 
> Hi Alexey,
> I'm not against further improvements to large directory handling (e.g.
> directory shrinking, implement pdirops through VFS, etc.) for ext4.
> That said, anything that changes the disk format should use a different
> feature flag than EXT4_FEATURE_INCOMPAT_LARGEDIR, since we have been
> using this flag in the Lustre code for several years already.
> 
> I think for very large directories that directory shrinking can be quite
> useful, and could actually be implemented without a format change since
> htree always masks off the top byte ("fullness ratio") of the logical block
> number for this reason, and removing leaf blocks does not change the other
> parts of the htree on-disk format.  This could still be done (in a slightly
> less efficient manner) even without "fullness ratio" (i.e. if fullness == 0,
> unset from older versions of ext4/e2fsck).  This would also help performance
> noticeably if a directory has many files deleted, as the htree index will
> shrink, and operations like readdir() will not have to skip empty blocks.
> 
> IMHO, I think the 3-level htree maximum limits are as far as we need to
> go for ext4.  With 4KB blocks this gives us a maximum directory size
> of about 5B entries, which is more files than can fit in the filesystem,
> Even for 1KB blocks the maximum directory size is about 8M entries, which
> is fine since 1KB blocksize is mostly only used for small filesystems, yet
> is still as good as what a 4KB filesystem can do today.
> 
> Cheers, Andreas
> 
>>> 17 марта 2017 г., в 0:44, Andreas Dilger <adilger@...ger.ca> написал(а):
>>> 
>>> On Mar 16, 2017, at 3:51 AM, Artem Blagodarenko <artem.blagodarenko@...il.com> wrote:
>>>> 
>>>> From: Artem Blagodarenko <artem.blagodarenko@...il.com>
>>>> 
>>>> This INCOMPAT_LARGEDIR feature allows larger directories to be created
>>>> in ldiskfs, both with directory sizes over 2GB and and a maximum htree
>>>> depth of 3 instead of the current limit of 2. These features are needed
>>>> in order to exceed the current limit of approximately 10M entries in a
>>>> single directory.
>>> 
>>> Artem,
>>> many thanks for updating and submitting this, and creating the e2fsck patches.
>>> 
>>> Ted,
>>> can you please add the original author for the largedir ext4 patch when
>>> landing this patch: Liang Zhen <liang.zhen@...el.com>
>>> 
>>> and these tags which contain more background information on this feature:
>>> 
>>> Lustre-change: https://review.hpdd.intel.com/375
>>> Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-50
>>> 
>>>> Signed-off-by: Yang Sheng <yang.sheng@...el.com>
>>>> Signed-off-by: Artem Blagodarenko <artem.blagodarenko@...gate.com>
>>> 
>>> Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>
>>> 
>>>> ---
>>>> fs/ext4/ext4.h  |  23 ++++++++---
>>>> fs/ext4/inode.c |   4 +-
>>>> fs/ext4/namei.c | 118 +++++++++++++++++++++++++++++++++++++++-----------------
>>>> 3 files changed, 102 insertions(+), 43 deletions(-)
>>>> 
>>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>>>> index 01d52b9..0bbbd9b 100644
>>>> --- a/fs/ext4/ext4.h
>>>> +++ b/fs/ext4/ext4.h
>>>> @@ -1799,7 +1799,8 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
>>>> 					 EXT4_FEATURE_INCOMPAT_MMP | \
>>>> 					 EXT4_FEATURE_INCOMPAT_INLINE_DATA | \
>>>> 					 EXT4_FEATURE_INCOMPAT_ENCRYPT | \
>>>> -					 EXT4_FEATURE_INCOMPAT_CSUM_SEED)
>>>> +					 EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
>>>> +					 EXT4_FEATURE_INCOMPAT_LARGEDIR)
>>>> #define EXT4_FEATURE_RO_COMPAT_SUPP	(EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
>>>> 					 EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
>>>> 					 EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \
>>>> @@ -2125,6 +2126,16 @@ struct dir_private_info {
>>>> */
>>>> #define ERR_BAD_DX_DIR	(-(MAX_ERRNO - 1))
>>>> 
>>>> +/* htree levels for ext4 */
>>>> +#define	EXT4_HTREE_LEVEL_COMPAT	2
>>>> +#define	EXT4_HTREE_LEVEL	3
>>>> +
>>>> +static inline int ext4_dir_htree_level(struct super_block *sb)
>>>> +{
>>>> +	return ext4_has_feature_largedir(sb) ?
>>>> +		EXT4_HTREE_LEVEL : EXT4_HTREE_LEVEL_COMPAT;
>>>> +}
>>>> +
>>>> /*
>>>> * Timeout and state flag for lazy initialization inode thread.
>>>> */
>>>> @@ -2758,13 +2769,15 @@ static inline void ext4_r_blocks_count_set(struct ext4_super_block *es,
>>>> 	es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
>>>> }
>>>> 
>>>> -static inline loff_t ext4_isize(struct ext4_inode *raw_inode)
>>>> +static inline loff_t ext4_isize(struct super_block *sb,
>>>> +				struct ext4_inode *raw_inode)
>>>> {
>>>> -	if (S_ISREG(le16_to_cpu(raw_inode->i_mode)))
>>>> +	if (ext4_has_feature_largedir(sb) ||
>>>> +	    S_ISREG(le16_to_cpu(raw_inode->i_mode)))
>>>> 		return ((loff_t)le32_to_cpu(raw_inode->i_size_high) << 32) |
>>>> 			le32_to_cpu(raw_inode->i_size_lo);
>>>> -	else
>>>> -		return (loff_t) le32_to_cpu(raw_inode->i_size_lo);
>>>> +
>>>> +	return (loff_t) le32_to_cpu(raw_inode->i_size_lo);
>>>> }
>>>> 
>>>> static inline void ext4_isize_set(struct ext4_inode *raw_inode, loff_t i_size)
>>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>>> index f622d4a..5787f3d 100644
>>>> --- a/fs/ext4/inode.c
>>>> +++ b/fs/ext4/inode.c
>>>> @@ -4682,7 +4682,7 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
>>>> 	if (ext4_has_feature_64bit(sb))
>>>> 		ei->i_file_acl |=
>>>> 			((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
>>>> -	inode->i_size = ext4_isize(raw_inode);
>>>> +	inode->i_size = ext4_isize(sb, raw_inode);
>>>> 	if ((size = i_size_read(inode)) < 0) {
>>>> 		EXT4_ERROR_INODE(inode, "bad i_size value: %lld", size);
>>>> 		ret = -EFSCORRUPTED;
>>>> @@ -5008,7 +5008,7 @@ static int ext4_do_update_inode(handle_t *handle,
>>>> 		raw_inode->i_file_acl_high =
>>>> 			cpu_to_le16(ei->i_file_acl >> 32);
>>>> 	raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
>>>> -	if (ei->i_disksize != ext4_isize(raw_inode)) {
>>>> +	if (ei->i_disksize != ext4_isize(inode->i_sb, raw_inode)) {
>>>> 		ext4_isize_set(raw_inode, ei->i_disksize);
>>>> 		need_datasync = 1;
>>>> 	}
>>>> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
>>>> index 6ad612c..3298fe3 100644
>>>> --- a/fs/ext4/namei.c
>>>> +++ b/fs/ext4/namei.c
>>>> @@ -513,7 +513,7 @@ static inline int ext4_handle_dirty_dx_node(handle_t *handle,
>>>> 
>>>> static inline ext4_lblk_t dx_get_block(struct dx_entry *entry)
>>>> {
>>>> -	return le32_to_cpu(entry->block) & 0x00ffffff;
>>>> +	return le32_to_cpu(entry->block) & 0x0fffffff;
>>>> }
>>> 
>>> It wouldn't be terrible to add a comment to this function explaining why
>>> the block numbers are masked off, which is to allow the high bits of the
>>> logical block number to hold a "fullness" fraction so that the kernel
>>> could start shrinking directories if many files are deleted.  That said,
>>> this isn't a shortcoming of this patch, but a suggestion if the patch is
>>> being resubmitted for some other reason.
>>> 
>>>> static inline void dx_set_block(struct dx_entry *entry, ext4_lblk_t value)
>>>> @@ -739,6 +739,7 @@ struct stats dx_show_entries(struct dx_hash_info *hinfo, struct inode *dir,
>>>> 	struct dx_frame *ret_err = ERR_PTR(ERR_BAD_DX_DIR);
>>>> 	u32 hash;
>>>> 
>>>> +	memset(frame_in, 0, EXT4_HTREE_LEVEL * sizeof(frame_in[0]));
>>>> 	frame->bh = ext4_read_dirblock(dir, 0, INDEX);
>>>> 	if (IS_ERR(frame->bh))
>>>> 		return (struct dx_frame *) frame->bh;
>>>> @@ -768,9 +769,15 @@ struct stats dx_show_entries(struct dx_hash_info *hinfo, struct inode *dir,
>>>> 	}
>>>> 
>>>> 	indirect = root->info.indirect_levels;
>>>> -	if (indirect > 1) {
>>>> -		ext4_warning_inode(dir, "Unimplemented hash depth: %#06x",
>>>> -				   root->info.indirect_levels);
>>>> +	if (indirect >= ext4_dir_htree_level(dir->i_sb)) {
>>>> +		ext4_warning(dir->i_sb,
>>>> +			     "Directory (ino: %lu) htree depth %#06x exceed"
>>>> +			     "supported value", dir->i_ino,
>>>> +			     ext4_dir_htree_level(dir->i_sb));
>>>> +		if (ext4_dir_htree_level(dir->i_sb) < EXT4_HTREE_LEVEL) {
>>>> +			ext4_warning(dir->i_sb, "Enable large directory "
>>>> +						"feature to access it");
>>>> +		}
>>>> 		goto fail;
>>>> 	}
>>>> 
>>>> @@ -859,12 +866,19 @@ struct stats dx_show_entries(struct dx_hash_info *hinfo, struct inode *dir,
>>>> 
>>>> static void dx_release(struct dx_frame *frames)
>>>> {
>>>> +	struct dx_root_info *info;
>>>> +	int i;
>>>> +
>>>> 	if (frames[0].bh == NULL)
>>>> 		return;
>>>> 
>>>> -	if (((struct dx_root *)frames[0].bh->b_data)->info.indirect_levels)
>>>> -		brelse(frames[1].bh);
>>>> -	brelse(frames[0].bh);
>>>> +	info = &((struct dx_root *)frames[0].bh->b_data)->info;
>>>> +	for (i = 0; i <= info->indirect_levels; i++) {
>>>> +		if (frames[i].bh == NULL)
>>>> +			break;
>>>> +		brelse(frames[i].bh);
>>>> +		frames[i].bh = NULL;
>>>> +	}
>>>> }
>>>> 
>>>> /*
>>>> @@ -1050,7 +1064,7 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
>>>> {
>>>> 	struct dx_hash_info hinfo;
>>>> 	struct ext4_dir_entry_2 *de;
>>>> -	struct dx_frame frames[2], *frame;
>>>> +	struct dx_frame frames[EXT4_HTREE_LEVEL], *frame;
>>>> 	struct inode *dir;
>>>> 	ext4_lblk_t block;
>>>> 	int count = 0;
>>>> @@ -1517,7 +1531,7 @@ static struct buffer_head * ext4_dx_find_entry(struct inode *dir,
>>>> 			struct ext4_dir_entry_2 **res_dir)
>>>> {
>>>> 	struct super_block * sb = dir->i_sb;
>>>> -	struct dx_frame frames[2], *frame;
>>>> +	struct dx_frame frames[EXT4_HTREE_LEVEL], *frame;
>>>> 	const struct qstr *d_name = fname->usr_fname;
>>>> 	struct buffer_head *bh;
>>>> 	ext4_lblk_t block;
>>>> @@ -1947,7 +1961,7 @@ static int add_dirent_to_buf(handle_t *handle, struct ext4_filename *fname,
>>>> 	 */
>>>> 	dir->i_mtime = dir->i_ctime = current_time(dir);
>>>> 	ext4_update_dx_flag(dir);
>>>> -	dir->i_version++;
>>>> +	inode_inc_iversion(dir);
>>>> 	ext4_mark_inode_dirty(handle, dir);
>>>> 	BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
>>>> 	err = ext4_handle_dirty_dirent_node(handle, dir, bh);
>>>> @@ -1966,7 +1980,7 @@ static int make_indexed_dir(handle_t *handle, struct ext4_filename *fname,
>>>> {
>>>> 	struct buffer_head *bh2;
>>>> 	struct dx_root	*root;
>>>> -	struct dx_frame	frames[2], *frame;
>>>> +	struct dx_frame	frames[EXT4_HTREE_LEVEL], *frame;
>>>> 	struct dx_entry *entries;
>>>> 	struct ext4_dir_entry_2	*de, *de2;
>>>> 	struct ext4_dir_entry_tail *t;
>>>> @@ -2185,13 +2199,16 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
>>>> static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> 			     struct inode *dir, struct inode *inode)
>>>> {
>>>> -	struct dx_frame frames[2], *frame;
>>>> +	struct dx_frame frames[EXT4_HTREE_LEVEL], *frame;
>>>> 	struct dx_entry *entries, *at;
>>>> 	struct buffer_head *bh;
>>>> 	struct super_block *sb = dir->i_sb;
>>>> 	struct ext4_dir_entry_2 *de;
>>>> +	int restart;
>>>> 	int err;
>>>> 
>>>> +again:
>>>> +	restart = 0;
>>>> 	frame = dx_probe(fname, dir, NULL, frames);
>>>> 	if (IS_ERR(frame))
>>>> 		return PTR_ERR(frame);
>>>> @@ -2213,24 +2230,44 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> 	if (err != -ENOSPC)
>>>> 		goto cleanup;
>>>> 
>>>> +	err = 0;
>>>> 	/* Block full, should compress but for now just split */
>>>> 	dxtrace(printk(KERN_DEBUG "using %u of %u node entries\n",
>>>> 		       dx_get_count(entries), dx_get_limit(entries)));
>>>> 	/* Need to split index? */
>>>> 	if (dx_get_count(entries) == dx_get_limit(entries)) {
>>>> 		ext4_lblk_t newblock;
>>>> -		unsigned icount = dx_get_count(entries);
>>>> -		int levels = frame - frames;
>>>> +		int levels = frame - frames + 1;
>>>> +		unsigned int icount;
>>>> +		int add_level = 1;
>>>> 		struct dx_entry *entries2;
>>>> 		struct dx_node *node2;
>>>> 		struct buffer_head *bh2;
>>>> 
>>>> -		if (levels && (dx_get_count(frames->entries) ==
>>>> -			       dx_get_limit(frames->entries))) {
>>>> -			ext4_warning_inode(dir, "Directory index full!");
>>>> +		while (frame > frames) {
>>>> +			if (dx_get_count((frame - 1)->entries) <
>>>> +			    dx_get_limit((frame - 1)->entries)) {
>>>> +				add_level = 0;
>>>> +				break;
>>>> +			}
>>>> +			frame--; /* split higher index block */
>>>> +			at = frame->at;
>>>> +			entries = frame->entries;
>>>> +			restart = 1;
>>>> +		}
>>>> +		if (add_level && levels == ext4_dir_htree_level(sb)) {
>>>> +			ext4_warning(sb, "Directory (ino: %lu) index full, "
>>>> +					 "reach max htree level :%d",
>>>> +					 dir->i_ino, levels);
>>>> +			if (ext4_dir_htree_level(sb) < EXT4_HTREE_LEVEL) {
>>>> +				ext4_warning(sb, "Large directory feature is "
>>>> +						 "not enabled on this "
>>>> +						 "filesystem");
>>>> +			}
>>>> 			err = -ENOSPC;
>>>> 			goto cleanup;
>>>> 		}
>>>> +		icount = dx_get_count(entries);
>>>> 		bh2 = ext4_append(handle, dir, &newblock);
>>>> 		if (IS_ERR(bh2)) {
>>>> 			err = PTR_ERR(bh2);
>>>> @@ -2245,7 +2282,7 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> 		err = ext4_journal_get_write_access(handle, frame->bh);
>>>> 		if (err)
>>>> 			goto journal_error;
>>>> -		if (levels) {
>>>> +		if (!add_level) {
>>>> 			unsigned icount1 = icount/2, icount2 = icount - icount1;
>>>> 			unsigned hash2 = dx_get_hash(entries + icount1);
>>>> 			dxtrace(printk(KERN_DEBUG "Split index %i/%i\n",
>>>> @@ -2253,7 +2290,7 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> 
>>>> 			BUFFER_TRACE(frame->bh, "get_write_access"); /* index root */
>>>> 			err = ext4_journal_get_write_access(handle,
>>>> -							     frames[0].bh);
>>>> +							     (frame - 1)->bh);
>>>> 			if (err)
>>>> 				goto journal_error;
>>>> 
>>>> @@ -2269,17 +2306,23 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> 				frame->entries = entries = entries2;
>>>> 				swap(frame->bh, bh2);
>>>> 			}
>>>> -			dx_insert_block(frames + 0, hash2, newblock);
>>>> -			dxtrace(dx_show_index("node", frames[1].entries));
>>>> +			dx_insert_block((frame - 1), hash2, newblock);
>>>> +			dxtrace(dx_show_index("node", frame->entries));
>>>> 			dxtrace(dx_show_index("node",
>>>> 			       ((struct dx_node *) bh2->b_data)->entries));
>>>> 			err = ext4_handle_dirty_dx_node(handle, dir, bh2);
>>>> 			if (err)
>>>> 				goto journal_error;
>>>> 			brelse (bh2);
>>>> +			ext4_handle_dirty_metadata(handle, dir,
>>>> +						   (frame - 1)->bh);
>>>> +			if (restart) {
>>>> +				ext4_handle_dirty_metadata(handle, dir,
>>>> +							   frame->bh);
>>>> +				goto cleanup;
>>>> +			}
>>>> 		} else {
>>>> -			dxtrace(printk(KERN_DEBUG
>>>> -				       "Creating second level index...\n"));
>>>> +			struct dx_root *dxroot;
>>>> 			memcpy((char *) entries2, (char *) entries,
>>>> 			       icount * sizeof(struct dx_entry));
>>>> 			dx_set_limit(entries2, dx_node_limit(dir));
>>>> @@ -2287,19 +2330,17 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> 			/* Set up root */
>>>> 			dx_set_count(entries, 1);
>>>> 			dx_set_block(entries + 0, newblock);
>>>> -			((struct dx_root *) frames[0].bh->b_data)->info.indirect_levels = 1;
>>>> -
>>>> -			/* Add new access path frame */
>>>> -			frame = frames + 1;
>>>> -			frame->at = at = at - entries + entries2;
>>>> -			frame->entries = entries = entries2;
>>>> -			frame->bh = bh2;
>>>> -			err = ext4_journal_get_write_access(handle,
>>>> -							     frame->bh);
>>>> -			if (err)
>>>> -				goto journal_error;
>>>> +			dxroot = (struct dx_root *)frames[0].bh->b_data;
>>>> +			dxroot->info.indirect_levels += 1;
>>>> +			dxtrace(printk(KERN_DEBUG
>>>> +				       "Creating %d level index...\n",
>>>> +				       info->indirect_levels));
>>>> +			ext4_handle_dirty_metadata(handle, dir, frame->bh);
>>>> +			ext4_handle_dirty_metadata(handle, dir, bh2);
>>>> +			brelse(bh2);
>>>> +			restart = 1;
>>>> +			goto cleanup;
>>>> 		}
>>>> -		err = ext4_handle_dirty_dx_node(handle, dir, frames[0].bh);
>>>> 		if (err) {
>>>> 			ext4_std_error(inode->i_sb, err);
>>>> 			goto cleanup;
>>>> @@ -2318,6 +2359,11 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>>>> cleanup:
>>>> 	brelse(bh);
>>>> 	dx_release(frames);
>>>> +	/* @restart is true means htree-path has been changed, we need to
>>>> +	 * repeat dx_probe() to find out valid htree-path
>>>> +	 */
>>>> +	if (restart && err == 0)
>>>> +		goto again;
>>>> 	return err;
>>>> }
>>>> 
>>>> @@ -2354,7 +2400,7 @@ int ext4_generic_delete_entry(handle_t *handle,
>>>> 					blocksize);
>>>> 			else
>>>> 				de->inode = 0;
>>>> -			dir->i_version++;
>>>> +			inode_inc_iversion(dir);
>>>> 			return 0;
>>>> 		}
>>>> 		i += ext4_rec_len_from_disk(de->rec_len, blocksize);
>>>> --
>>>> 1.8.3.1
>>>> 
>>> 
>>> 
>>> Cheers, Andreas
>>> 
>>> 
>>> 
>>> 
>>> 
>> 
> 
> 
> Cheers, Andreas
> 
> 
> 
> 
> 

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